History ThouShaltNotKill / TheDCU

* Averted in ''Film/SupermanII'', where Superman smiles as he throws Zod down a pit to his death.

* ''WesternAnimation/BatmanTheAnimatedSeries'': Much like the rest of the franchise, Bruce enforces this trope, though there are times when he comes dangerously close to breaking this rule.
** In "[[Recap/BatmanTheAnimatedSeriesE6TheUnderdwellers The Underdwellers]]", the villain Sewer King uses a small army of abandoned children to steal and commit crime for him, punishing them cruelly when they fail. Batman, furious about this, corners him at the end of the episode. He saves him from an incoming train. When the Sewer King hysterically asks why, Batman angrily responses that although he realizes that passing judgment is a matter for the courts, he was ''sorely tempted'' to take matters into his own hands.
** In "[[Recap/BatmanTheAnimatedSeriesE62HisSiliconSoul His Silicon Soul]]", the robot copy of Batman that Hardac created in a final attempt to gain revenge on Batman and KillAllHumans follows his human template's example all too well. The robot has a HeroicBSOD when it thinks it killed Batman during their fight and sacrifices itself to foil the scheme it had earlier set in motion when it realizes more people will die because of it.
* In ''WesternAnimation/BatmanBeyond'', Terry seems to have an attitude somewhat similar to the ''Film/BatmanBegins'' version of Batman: the series makes it a specific point that he won't kill in cold blood, and he generally tries to make sure his villains rot in jail, but he often won't go very far out of his way to save them, either. He's also consistently willing to use lethal force in the heat of combat, usually in the form of [[CombatPragmatist combat pragmatism]] such as chucking handy barrels of toxic waste.
* In ''WesternAnimation/JusticeLeague'', an alternate universe episode sees the Flash die by Lex Luthor's hand, to which Superman responds by killing his archvillain in a gruesome fashion. These events eventually draw the default universe's Lex Luthor to try to ruin Superman by goading him into the same murderous rage. Late in this arc, the Flash appears to sacrifice himself to stop Lex's grandest scheme, to which Lex defiantly gloats. Superman hoists Luthor in front of his face and bitterly growls, "I'm ''not'' the Superman who killed Lex Luthor. Right now, I wish to heaven I were, but I'm ''not''."
** The prime universe Superman made an exception for Darkseid in "Twilight". After Darkseid's latest gambit to conquer the universe, Superman has had it with the tyrant and stays behind on the exploding asteroid so he can kill Darkseid with his bare hands. The only reason he doesn't manage it is because Batman pulls him and Orion into a Boom Tube to save them. As it stands, Superman does manage to kill Darkseid by trapping him on the self-destructing asteroid. It even sticks for four whole seasons. Notably, he spared Darkseid the first time he beat him, and this is when Darkseid had nearly (indirectly) killed Supergirl. Kara herself had to persuade him from killing Darkseid that time though.
** The League doesn't seem to adhere to this rule under wartime conditions. In "The Savage Time," every member of the Justice League present commits clearly lethal actions in battle against the Nazis, and with the Green Lantern ring out of commission, John uses an ordinary rifle like any other Marine. Similarly, in the pilot, nobody bats an eye at killing Imperium aliens, and when fighting Thanagarians, the League are willing to use deadly force as well.
** In the series finale, Superman subtly expresses his hopes that Darkseid and Lex Luthor are dead for good, without his having to kill them. He is so hopeful that five of the other founding seven have to [[DeathIsCheap convince him otherwise.]] According to WordOfGod, [[spoiler: Superman was actually right this time. Darkseid and Luthor both became part of the Source Wall.]]

* In ''WesternAnimation/TeenTitansTroubleInTokyo'' Robin gets in some trouble with the law when it looks like he killed the supervillain he was fighting. In [[WesternAnimation/TeenTitans the series itself]], however, the episode "Aftershock" [[AvertedTrope averts]] this trope. While the other Titans were holding back, Raven's words and actions indicate she was genuinely trying to kill Terra when they fought. Later [[spoiler:Terra decides to pull a HeelFaceTurn and stops working for the villain Slade; she accomplishes this by throwing Slade into a pit of lava.]]

* Maintaining the same belief in the comics, Batman in ''VideoGame/BatmanArkhamAsylum'' never kills. According to his detective mode, his enemies always wind up unconscious. Yes, even the ones who have been punched in the face, or had a wall they were standing in front of blown up. Unconscious, every one.

** [[https://www.youtube.com/watch?v=hCl0Qv8DkvQ As pointed out by Outside XBox]], the people Batman nails in the head with propane tanks, drags off the GCPD roof to a multi-storey fall, pummels in the face at point-blank with "less-than-lethal" ammunition, or clonks in the throat with a car door should really not be as alive as Detective Mode claims they are.
*** [[https://youtu.be/XXyrRdDlE-0?t=215 Outside XBox also pointed out]] that there were two times in Arkham Origins where Batman [[MurderByInaction could have let the Joker die and the blood technically wouldn't be on his hands]], [[LoopholeAbuse meaning that the Joker would be out of the picture without Batman technically violating the trope.]] [[spoiler: First was when they first met and Bane blasted the Joker off of a rooftop, the second time was the above mentioned electric chair scenario. In both cases, the Joker's death would have been on ''Bane'' and Batman could have walked away guilt-free, [[SaveTheVillain but nope.]]]]
** In ''VideoGame/BatmanArkhamKnight'', some soldiers in the Arkham Knight's militia start exploiting Batman's refusal to kill by wearing suicide vests that are programmed to explode and kill the wearer if they become unconscious. Against Batman, this is probably better protection than any body armour you can get.
* In the NES Batman game, Batman averts movie canon and hurls the Joker off the cathedral. [[HesDeadJim The rest of the ending is spent zooming in on the Joker's corpse.]] Then it plays it straight with the [[DirectToVideo NES only sequel]], ''Batman: Return of the Joker''.
* {{Deconstructed}} in both ''VideoGame/InjusticeGodsAmongUs'' and ''VideoGame/Injustice2''. Batman thinks killing in the name of justice would make him no different from the criminals he or the Justice League frequently deal with but wasn't able to end ComicBook/TheJoker's KarmaHoudini problem, which backfired horribly when the MonsterClown killed millions in Metropolis in a scheme to drive Superman to a FaceHeelTurn. He insists on applying this rule out [[ControlFreak of his]] [[ItsAllAboutMe own ego]] even when he's outclassed by the likes of Darkseid or Brainiac, but [[LameComeback can't respond]] when the Regime members [[VillainHasAPoint all but]] [[ArmorPiercingQuestion accuse him of]] MurderByInaction by asking how many innocents must die before realizing his no-kill rule is ineffective and that MurderIsTheBestSolution, or how his misplaced leniency has caused villains like Gorilla Grodd to keep on breaking out of {{Cardboard Prison}}s like Arkham and terrorize society with [[JokerImmunity no impunity]], despite knowing they [[ChronicVillainy won't reform]] no matter how many chances they're offered, as it only worsens their behavior. Believing traditional superheroics to be outdated, the Regime remnants see Batman's refusal to kill as a sign of weakness and think the ethical framework that lets criminals alive is too ineffectual. They also call him a {{hypocrite}}, in that while he won't kill, traumatic brain knock-outs are fine, but he never finds out if they survived said injuries.

** Deconstructed[[note]]Along with [[DeconstructorFleet many other tropes, superhero-based or otherwise]][[/note]] in ''Film/ManOfSteel'', where Superman is placed in an impossible situation where, [[spoiler:General Zod, enraged beyond reason, has sworn he will ''never stop killing'' humans in an effort to hurt Kal-El for preventing the rebirth of Krypton. There is no super prison, no gateway left to the PhantomZone -- just Kal, Zod, and a family of four about to be incinerated by Zod's rampage...so he ''breaks Zod's neck''.]] This is not an action he undertakes lightly however, as the following scene shows. Expanding on this, WordOfGod says that in the ''Man of Steel'' continuity, [[spoiler:this incident is ''why'' Superman swears never to kill anyone: he knows first-hand what a terrible, traumatic thing it is to take a life.]]

*** Batman as one would [[AuthorAppeal expect]] for a DarkerAndEdgier director like Creator/ZackSnyder, the Dark Knight in ''Batman V Superman Dawn Of Justice'' is shown both killing mooks indiscriminately and [[MurderArsonAndJaywalking even using firearms]]. There is some level of justification as this Batman in particular is jaded past the point of a DespairEventHorizon after the death of Robin and Wayne manor getting burned down. DCEU Batman only plays this straight in regards to Superman as Clark's words about Martha put an end to his determination to murder Supes and Batman also spares Lex Luthor at the end, although there's FridgeLogic with the latter as DCEU Batman has no qualms [[WhatMeasureIsAMook about killing henchmen]] just doing their jobs and yet shows mercy to Lex as well as Joker who are both unrepentant psychopaths. Then again you can argue it is pretty justified given the henchmen Batman kills in this movie are all heavily-armed international mercenaries who are in the business of doing things like massacring entire villages - in both threat level and repugnance they're quite a few steps above Gotham's street criminals.

* ''Series/{{Arrow}}'':
** After five or so years of semi-righteous [[TheStraightAndArrowPath murder]] left and right, [[AntiHero Oliver]] [[TheCowl Queen]] attempts to do his vigilante work with [[HeroicVow less collateral damage]] (barring that of [[HeroInsurance property]], of course) after [[HeroicBSOD Tommy's death]]. However, this trope is danced around, as he [[UnstoppableRage instinctively]] [[NoKillLikeOverkill puts three arrows]] in [[EvilIsHammy Count Vertigo]] when the latter [[ForTheEvulz grinningly]] [[AndYourLittleDogToo threatens]] [[TheHeart Felicity]]. And all this mere weeks after the vow is made, too. His resolve is nowhere near as strong as that of [[Franchise/{{Superman}} his]] [[Franchise/{{Batman}} counterparts]].

** Since then, he mostly keeps to the rule, only killing when absolutely necessary. What causes him to actually backslide is [[MyGreatestFailure Laurel's]] [[LivingEmotionalCrutch death]] in Season 4. Not only does he kill her murderer Damien Darkh, he almost discards the rule entirely, only going back to his previous provision of killing when necessary after a talk with Thea and the TraumaCongaLine that is the latter half of Season 5.
* In ''Series/TheFlash2014'', Leonard Snart/Captain Cold is a petty thief turned supervillain who doesn't kill if he can help it but will if forced to or crossed. This is mostly out of [[PragmaticVillainy pragmatism]] rather than any kind of morality, as he finds the consequences of murder more trouble than they're usually worth. After Flash challenges him to continue his supervillain career without killing anyone, he accepts, seeing it as a true test of his skills.

* ''Series/{{Supergirl|2015}}'': Supergirl follows the same general "Thou Shalt Not Kill" policy as her cousin, which has led to a few baddies escaping. That does not mean she has not had to destroy a few alien baddies from time to time, and she also destroys the Red Tornado in a fit of anger, not realizing that he'd become sentient a few moments before. The rule is decidedly ''not'' followed by her DEO colleagues, including her sister, Alex, who is a trained killer and uses such skills on more than one occasion. The Guardian, although he delivers Daredevil-style beatdowns on bad guys, also adheres to Supergirl's no-killing rule.

* Deconstructed[[note]]Along with [[DeconstructorFleet many other tropes, superhero-based or otherwise]][[/note]] in ''Film/ManOfSteel'', where Superman is placed in an impossible situation where, [[spoiler:General Zod, enraged beyond reason, has sworn he will ''never stop killing'' humans in an effort to hurt Kal-El for preventing the rebirth of Krypton. There is no super prison, no gateway left to the PhantomZone -- just Kal, Zod, and a family of four about to be incinerated by Zod's rampage...so he ''breaks Zod's neck''.]] This is not an action he undertakes lightly however, as the following scene shows.
** Expanding on the above, WordOfGod says that in the ''Man of Steel'' continuity, [[spoiler:this incident is ''why'' Superman swears never to kill anyone: he knows first-hand what a terrible, traumatic thing it is to take a life.]]

* ComicBook/GreenArrow is a big believer in this. It's why he uses so many trick arrows, like the infamous boxing glove arrow, instead of actual arrows. The downward spiral that culminated in his first death started the night he actually killed someone. [[spoiler: He made an exception for Prometheus after the latter attacked Star City with a KillSat and killed thousands, including his granddaughter Lian Harper.]]

* ''Series/WonderWoman'': Wonder Woman declares in the pilot, "The New Original Wonder Woman", "Where I'm from we try never to hurt people". Aside from a couple of war-related incidents and [[TooPowerfulToLive an encounter with Hitler]] in "Anschluss 77", Wonder Woman's opponents are generally let off very lightly, especially considering [[StrongerThanTheyLook what she is capable of]]. She'd often let the [[{{Mooks}} hired thugs]] simply go since they're no threat.

** In "The Underdwellers", the villain Sewer King uses a small army of abandoned children to steal and commit crime for him, punishing them cruelly when they fail. Batman, furious about this, corners him at the end of the episode. He saves him from an incoming train. When the Sewer King hysterically asks why, Batman angrily responses that although he realizes that passing judgment is a matter for the courts, he was ''sorely tempted'' to take matters into his own hands.
** In "His Silicon Soul", the robot copy of Batman that Hardac created in a final attempt to gain revenge on Batman and KillAllHumans follows his human template's example all too well. The robot has a HeroicBSOD when it thinks it killed Batman during their fight and sacrifices itself to foil the scheme it had earlier set in motion when it realizes more people will die because of it.

* The bylaws of the ''ComicBook/LegionOfSuperHeroes'' firmly forbid killing any sentient -- unsurprising, since they were created during UsefulNotes/{{the Silver Age|OfComicBooks}}. The tradition has been retained throughout the Legion's various continuities; even in the DarkerAndEdgier ''Legion Lost'' limited series, Live Wire officially resigned from the Legion before performing a HeroicSacrifice to kill the Progenitor, an OmnicidalManiac with [[AGodAmI the power to control matter on a cosmic scale]], in order to allow his teammates to escape without the Progenitor following them back and taking over their universe.
** The Legion Constitution was once published in the comics, in its entirety. The section in question says that "[n]o Legionnaire shall take the life of any sapient being, save as a provable only alternative to the death of the Legionnaire, or the deaths of other sapient beings." The writers usually have the Legionnaires treat the question of lethal force more strictly than their constitution actually requires.

** The League doesn't seem to adhere to this rule under wartime conditions. In "The Savage Time," every member of the Justice League present committed clearly lethal actions in battle against the Nazis, and with the GreenLanternRing out of commission, John used an ordinary rifle like any other Marine. Similarly, in the pilot, nobody batted an eye at killing Imperium aliens, and when fighting Thanagarians, the League are willing to use deadly force as well.

* When ''ComicBook/TheFlash'' thought he killed Godspeed, whom he'd been insisting that real heroes never kill:
-->'''The Flash:''' ''(depressed)'' Heroes don't kill. We find a better way.

'''The Joker''': Aww, [[FoeYay so you DO think about me]]!\\

* The Franchise/GreenLantern Corps ''used'' to follow this policy. The Guardians revoked it during the ''ComicBook/SinestroCorpsWar''. [[spoiler:[[XanatosGambit Apparently this was Sinestro's goal all along.]] Whether the Sinestros won or lost, a more lethal and fearsome Corps would be policing the cosmos.]] Part of the writers' reasoning was that real-life police are permitted to shoot to kill; SpacePolice shouldn't be any different. The next few issues after the event explored the morality of giving the Lanterns this authority. Some Green Lanterns are against it, some are all for it, but neither side is presented as wrong and the ones against killing can't deny that being able to kill was the main reason they won the war. (Though needless murder is right out.)
** There was a subversion in the case of NinetiesAntiHero Jack T. Chance. When he discovered his GreenLanternRing would not let him use lethal force, [[LoopholeAbuse he adapted and started using a revolver to deliver the killing blow.]] The only reason the Guardians didn't throw him out was because nothing less had worked on his CrapsackWorld, and this policy was also why they didn't need to recruit a new lantern for his sector as quickly as they usually did as he was the first one in ages to have a sizeable tenure.

** The Nolan Film [[JustifiedTrope Justifies]] this (or at least tries to) because the last time he saved [[spoiler:Ra]]'s he came back and continued his KnightTemplar plan [[UngratefulBastard despite that]]. It's even lampshaded:

-->'''[[spoiler:Ra]]'s:''' "I warned you about compassion."

** Another fact to consider is that Batman ''personally threw'' the Joker off the building. If he didn't catch the Joker, then he explicitly killed him. But with [[spoiler:Ra]]'s, he willingly put himself on the train with the knowledge that Batman would try his absolute hardest to stop him. [[spoiler:Ra]]'s taught Batman everything he knows and remembers that one time that Bruce unintentionally burnt down an entire fortress to avoid killing. [[spoiler:Ra]]'s obviously understood the potential risk of going against Batman, and one could reasonably assume that he would have some sort of way to escape. Nolanverse's Batman follows the code that he will never intentionally kill a person, but if the bad guy puts himself into a position where s/he will be killed by collateral damage in the act of Batman saving Gotham / the innocent, and there is no way to save them, then there is nothing that can be done. [[spoiler:Ra]]'s had no way of saving himself on the mountain, but Bruce could save him, and so he did. On the train, Batman had reason to believe that [[spoiler:Ra]]'s could save himself, and the only choices were Batman and Gordon destroy the train, '''''or every living thing in Gotham dies.''''' The same exact problem comes up in Film/TheDarkKnightRises, when [[spoiler: the nuke will go off in less than ten minutes, the tanks are actively trying to kill Batman and Catwoman, they can't force the truck to go back to the generator, and all warning shots have failed to get the truck to stop. Either the truck and tanks are stopped with force, '''''or literally everything in Gotham is wiped off the face of the earth and the rest of the US gets hit by the fallout.''''']]

** This is in comparison to ''Film/BatmanTheMovie''. When Batman was trying to find a safe place to dispose of a bomb he refused to throw it where anybody could get hurt. Including at ducks. Later in the movie when he and Robin accidently kill some mooks they do mourn for them as they weren't expecting them to [[ItMakesSenseInContext combust]].

* ''Series/IronFist2017'': Claire believes this, though Colleen disagrees, and they argue about it.

!!Franchise/TheDCU

* The bylaws of the ''ComicBook/{{Legion of Super-Heroes}}'' firmly forbid killing any sentient -- unsurprising, since they were created during UsefulNotes/{{the Silver Age|OfComicBooks}}. The tradition has been retained throughout the Legion's various continuities; even in the DarkerAndEdgier ''Legion Lost'' limited series, Live Wire officially resigned from the Legion before performing a HeroicSacrifice to kill the Progenitor, an OmnicidalManiac with [[AGodAmI the power to control matter on a cosmic scale]], in order to allow his teammates to escape without the Progenitor following them back and taking over their universe.

** ''ComicBook/TheLegendOfWonderWoman2016'' brings Diana closer to her traditional viewpoint on this matter. She understands that soldiers kill but she herself will not even in the middle of a battle. It helps that the Duke of Deception's zombies give up the ghost upon being lassoed with the lasso of truth as whatever is animating them cannot stand the truth of their situation, which she does not see as killing them as they are not alive. While she does "kill" the Titan it is another being animated and run by spirits that are no longer housed in their original bodies and that have been twisted by being congealed together and "living" for so long.

* ''ComicBook/{{Supergirl}}'' also avoids killing:
** In the ''ComicBook/NewKrypton'' arc, Supergirl was horrified when she [[spoiler:accidentally killed Superwoman, even though Superwoman had tried to kill her several times.]]
** In the ''ComicBook/New52'' Supergirl does not know her own strength. She gets upset when her actions endanger people and is relieved once that she sees that nobody has been harmed.
** Subverted in ''ComicBook/RedDaughterOfKrypton''. Supergirl is horrified when she apparently kills mass murderer and hitman ''SelfDemonstrating/{{Lobo}}'' after kicking him. Then he takes advantage of her distress to catch her off guard, and almost fries her brains with an ultrasonic device. Right there and then she decides he has "got it coming".
** Subverted again at the end of that arc. She [[spoiler:executed an artificial, genocidal body-snatching alien abomination]] reasoning that "This is not murder. It is the end of a terrible mistake."
** Zigzagged in ''ComicBook/ElseworldsFinestSupergirlAndBatgirl''. Supergirl didn't like to kill… but when she discovered [[spoiler:that ''ComicBook/LexLuthor'' murdered her cousin]], she wanted to kill him. However ''ComicBook/{{Batgirl}}'' talked her out of it, stating that she's a hero and she mustn't drop to his level.
** She fully intended to kill the Anti-Monitor in ''ComicBook/CrisisOnInfiniteEarths'', with just a brief distraction getting her killed before she can kill him.

* Franchise/{{Superman}} has taken a solemn vow ''never'' to kill. Moral issues aside, there's a practical reason for his oath: a demigod who had no issues with killing [[BewareTheSuperman would never be trusted]], and would be considered a demagogue, not a hero. Several alternate versions of Superman, whether an What If? story or an alternate dimension of him, have explored a Superman who had no problems with lethal force.\\
\\
From a writing standpoint, keeping Superman an ActualPacifist makes it a stunning WhamShot should he actually be forced to kill, as mentioned in the very few cases where he had no alternative, and had exhausted ''all'' of the possibilities.
** It's strongly implied -- and outright used in ''ComicBook/WhateverHappenedToTheManOfTomorrow'' -- that he believes that he should give up being Superman if he takes a life. (He cannot kill himself, since his oath applies to himself as well. This was shown in a number of Bronze Age stories, including one where he is caught in a hallucination that supposedly shows the future and realizes that since it shows him killing himself, it must be false.)
--->'''Superman:''' I broke my oath. I killed him. Nobody has the right to kill. Not Mxyzptlk... not you... not Superman. '''Especially''' not Superman.
** ''Whatever Happened to the Man of Tomorrow'' also has SelfDemonstrating/{{Bizarro}} [[InvertedTrope go on a murderous rampage on the basis that he wants to be more closely the opposite of Superman]], though he's really being manipulated into thinking that by the BigBad. He also kills himself.
** A ComicBook/PostCrisis Franchise/{{Superman}} story had the hero face such a situation when an abusive husband, whom Supes gave a deserved thrashing, later murdered his wife. Superman later caught him secretly viewing her funeral and was sorely tempted to kill him right there and then. However, the relatives of both husband and wife began to plead for Superman to spare him and kill him respectively. Superman, holding the murderer while this argument is raging, painfully realized that he was in no position to make such monumental decisions and decided to simply hand the criminal to the police so the justice system can handle the matter.
** Another Superman story, ''ComicBook/WhatsSoFunnyAboutTruthJusticeAndTheAmericanWay'' famously had him forced to deal with the arrival of "The Elite" (a [[AlternateCompanyEquivalent thinly-veiled copy]] of ComicBook/TheAuthority), superheroes with absolutely no qualms about killing villains. Over the course of the issue, he watched them become more and more popular, despite (and indeed, ''because of'') their excessive use of force. In the end, he challenged them to a fight -- and proceeded (after giving them a HopeSpot) to subdue them more or less harmlessly. Though it sure dang LOOKED like he killed them, until he revealed that he used painful-looking non-lethal techniques. The story showed not only why does Superman not kill, but just how downright ''scary'' he would be if he did. The story eventually got an AdaptationExpansion into the made for DVD movie ''WesternAnimation/SupermanVsTheElite''.
** And another Superman story, ''ComicBook/TheSupergirlSaga'', had him actually killing (well, executing) three Kryptonians on an alternate Earth who had annihilated all life on the planet. Despite the circumstances which almost anyone else would deem it both just and necessary -- as they had committed the act of planetary murder, threatened to find an way to Superman's universe and do it again, and were stronger than he was -- the act haunted him for years. After he did it, he even developed a split personality and then exiled himself from Earth after he got that under control.
** This trope is somewhat justified in another story where Superman explains to the Ultramarines, a team of superheroes known for their use of lethal force, after the Justice League has pulled them out of a situation they were unable to handle, that their "'no-nonsense' solutions [[BackFromTheDead just don't hold water]] in a [[CrossoverCosmology complex]] [[FantasyKitchenSink world]] of [[EverythingsBetterWithMonkeys jet-powered apes]] and TimeTravel," as death apparently held less barriers for them, and in fact was more merciful, than some of the extreme incarceration punishments the League had to devise.
** Superman has shown to be one of the most extreme examples of never killing. In one case he saved ComicBook/{{Darkseid}}'s life (Darkseid helped him stop the threat that put him near death, granted, but come on, it's freaking ''Darkseid'') and in another instance, he was trapped in a dimension where he was forced to go to war with demons for a thousand years, but still refused to kill them. He even initially objected to Franchise/WonderWoman killing them, but didn't have an answer when she asked him what she was supposed to do.
** Though it's often overlooked, during his final fight with Doomsday at the end of ''ComicBook/TheDeathOfSuperman'' storyline, he was trying to kill him. If he hadn't, Doomsday likely would've destroyed Metropolis and everyone in it (although only in the last bit of the fight when he realized nothing else would even give the monster pause, which shocked Jimmy and Lois). It probably helps that Doomsday's mind was read a couple of times in the story, and was revealed to be nothing but rage and bloodlust. This was followed up in ''Hunter Prey'', as Superman, after finding out that Doomsday was now far more powerful than himself, and constantly growing in might, he could come up with no other available options than letting Waverider exile the beast to the end of the universe, to let entropy consume it. Doomsday was later rescued by ''ComicBook/{{Brainiac}}'', keeps coming back after being killed, and heals all other injuries instantly, so breaking his neck has the same effect as knocking a regular villain out, which, in combination with being more than Superman can handle upfront, is the reason why he can be the exception.
** ''ComicBook/KingdomCome'' revolved around the fact Superman abandoned humanity when he realized the public approved Magog's murder of ComicBook/TheJoker. Ross and Waid even broke their backs to make the kill visually parallel [[UsefulNotes/JohnFKennedy JFK]] assassin Lee Harvey Oswald's death at the hands of Jack Ruby, [[{{Anvilicious}} just in case anyone was thinking]] that maybe killing the guy who had just gassed the entire staff of the Daily Planet might not be such a bad thing. In the same series, Superman is disturbed by Wonder Woman wielding a sword; she snaps back that not everyone has ''heat vision''.
** In the pre-Crisis mini-series ''Phantom Zone'' penned by Creator/SteveGerber, Superman confronts General Zod, who laughs that Kal-El won't kill him. He's right. To quote: "I can't take your life, much as I'm tempted. But my code doesn't say a '''''damn''''' thing about not battering you to within an inch of it, ''murderer!''" Once Zod is out cold for a long, long time, Superman, still holding him by the tunic, thinks "And there are times I've considered chucking that code entirely."
** Played with in the ''ComicBook/{{Legion of Super-Heroes}}'' story "The Legionnaire Who Killed!" where the Legion decided whether to expel Star Boy for killing. Superman and the other Flying Bricks -- ComicBook/{{Supergirl}}, Mon-El and Ultra Boy -- voted to not expel him. The reason? Because it's easy for him, Superman, to have a code against killing when there aren't a lot of things that can hurt him, but other people may have different circumstances than him and he has no right to hold them to his code.
** Emphasizing Superman's adherence to his code is this: in the few official {{crossover}} series that exist, Superman has even refused to kill ''[[Franchise/{{Alien}} Xenomorphs]]''! For context, xenomorphs are a highly aggressive species of alien predators with no higher reasoning than basic animal instincts and a parasitic reproductive cycle, which are capable of causing ''planet-scale extinction events'' thanks to their voracious and insatiable need for living victims as food and hosts for their young. Even ''Batman'', himself a noted devotee of this rule, is willing to forgo it when xenomorphs are involved, and in the Superman/Batman/Aliens crossover (yes, this exists), actually calls Superman out on his willingness to spare such dangerous animals.
** It's not brought up much, but at the end of "Reign of the Superman" Superman outright kills Hank Henshaw (AKA Cyborg Superman) after the latter slaughtered Coast City, his reasoning being "You're dangerous, cyborg -- I doubt any prison can effectively protect society from you!". Henshaw does say that he will "somehow" survive Superman literally shattering him, but Superman himself doubts this and says "''if'' you do, Henshaw, I'll be waiting", indicating that he's fully expecting to kill Henshaw for good (or at least accepting that as one of two scenarios). Henshaw survives by storing a copy of his consciousness in a device in space and transferring it to Doomsday's body, but it doesn't change that Superman did literally kill him (terminating his vital functions), gave explicit and sound reasoning for why he did so, and was fine with him never coming back. It could be that Superman didn't see Henshaw as actually ''alive'', but a construct of the man he saw die back in his original appearance.
** In ''ComicBook/OurWorldsAtWar'' he helps kill both Imperiex and Brainiac 13 by sending them both back in time to the Big Bang; in ''ComicBook/FinalCrisis'', he is the one who finishes off Darkseid. In general his code is based on the fact that he is far more powerful than most of the villains he comes across and if he is capable of defeating them without resorting to violence, he will; on the flip-side, if you are an enemy who is as strong or stronger and you are sufficiently ruthless or dangerous enough that death is the only thing that will stop you...then yes, Superman ''will'' kill you. Helps if [[WhatMeasureIsANonHuman you aren't human, too.]]
** There were at least two [[UsefulNotes/TheBronzeAgeOfComicBooks Bronze Age]] stories in which criminals tricked Superman into believing he had accidentally killed someone, so that he would hang up his cape and stop fighting crime (in one, they tricked him into thinking he had accidentally killed ''ComicBook/LanaLang''!).
** This was the central point of the Bronze Age text novel ''Literature/MiracleMonday''. A demon called C.W. Saturn possesses a woman and causes havoc, trying to tempt Superman into stopping him by [[MercyKill killing her physical form]]. [[spoiler:If it had succeeded, Superman's soul would have been damned. Superman refuses, of course, and defeats the demon by constantly reversing its mischief until its time on Earth runs out.]]
** Superman was about to kill Mongul in ''ComicBook/ForTheManWhoHasEverything'', but seeing the statues of his parents stays his hand, and nearly gets him killed by Mongul. Fortunately, he was saved by Jason Todd dropping the LotusEaterMachine on Mongul.
** Golden Age Superman, though, subverted this. Although he didn't like killing, he wasn't above threatening criminals with death or letting them die. And during his final fight with the Anti-Monitor in ''ComicBook/CrisisOnInfiniteEarths'', he had to do everything to put an end to the villain's threat once and for all.

* ThouShaltNotKill/Franchise/{{Superman}}

* ''Franchise/{{Batman}}'' is the poster boy for this trope. In fact, it's been heavily implied that his almost psychotic compulsion to never kill is the only thing keeping him from being one of the psychopaths he regularly fights -- he has outright stated that he fears if he started, he would never stop. Famously, Batman [[EarlyInstallmentWeirdness was willing to kill]] in the first year of his existence. As early as ''Batman'' #4 in 1940, he was declaring "We never kill with weapons of any kind." Because of this trope, BatmanGrabsAGun is an easy way to convey just how serious a threat a villain is.
** In the {{Novelization}} of ''ComicBook/{{Knightfall}}'', Gordon in an internal monologue reveals he only tolerates Bats because he doesn't kill. The moment he crosses the line, according to Gordon, he'll be marked as a criminal like any other and his relationship with him will be over.
** ''ComicBook/FinalCrisis'' has [[IncrediblyLamePun finally]] shown us the only person so evil and dangerous Batman was willing to kill him: [[spoiler: Darkseid. Which just makes the Superman example above even funnier]]. By the time Batman kills [[spoiler: Darkseid]] the villain has taken several [[TookALevelInBadass levels in badass]], and [[spoiler: was destroying the entire universe ''just by existing''. Whereas Superman saved an alien warlord, but this point it's one life against ''all of time and space'']]. It also helped Bats that he himself was going to die, so it was probably in his mind a fitting punishment for breaking his oath.
** The Creator/TimBurton Batman movies disregard this entirely, with Batman frequently killing both henchmen and the central villains (It's not like though he had any alternative in most cases). In ''Film/TheDarkKnightTrilogy'' Batman refuses to kill anyone, but he is generally [[HighAltitudeInterrogation more than happy to come scarily close to frighten someone, without actually crossing the line.]] This is demonstrated best during ''Film/TheDarkKnight''.
--->'''Salvatore Maroni:''' From this height, the fall wouldn't kill me.\\
'''Batman:''' I'm counting on it.
*** He ''does'' engage in some LoopholeAbuse in ''Film/BatmanBegins'', when [[spoiler: he comments to Ra's al-Ghul that "I won't kill you... [[RefuseToRescueTheDisliked but I don't have to save you]]" before leaving him to his fate]].
** ''ComicBook/{{Flashpoint}}'' Batman [[spoiler: aka Thomas Wayne]] dispenses with this altogether and shows himself to be an exceptionally violent and uncompromising psychopath who has killed off a good portion of the villains in that timeline and threatens to use lethal force all the time.
*** Similarly, his ''ComicBook/Earth2'' counterpart is more than willing to kill, and it's what tips Lois Lane off that the Batman in front of her ''isn't'' Bruce Wayne, since the ''Earth 2'' Lois was in on his SecretIdentity and was very close to him and his wife.
** In the {{Novelization}} of ''ComicBook/{{Knightfall}}'', Batman's use of violence is explored. A monk refuses to teach Batman some of the most secret fighting techniques because he won't foreswear violence. Lady Shiva teaches Batman to fight again, but is mildly offended and amused when Batman learns how to ''enjoy'' violence again, but won't cross the line into lethal violence. Bruce has a startled, depressing EurekaMoment when he realizes that he'd always ''loved'' the violence, despite what he told himself.
*** This is sometimes used to explain why Batman is so adamant in his refusal to kill: he's afraid that he would come to enjoy the killing and become just another costumed serial killer.
** Cassandra Cain[=/=]ComicBook/{{Batgirl|2000}} III had an even deeper aversion to killing as she could read human body language perfectly. After seeing death once she vowed to never see it again and tried to save a death row inmate to uphold that oath.
** This is so inherent to his character that it's called '[[TropeNamers the Batman rule]]' by other characters, specifically ComicBook/{{Batwoman}} and her father.
** He came ''very'' close to breaking his oath in ''ComicBook/BatmanNoMansLand''. After the Joker murdered Gordon's wife, Batman still refused to kill him, but told Jim he would ''not'' stop him from doing so. (And Jim ''almost'' did, restraining himself only because there had been too much death already.)
** Batman will often take this trope to extremes. Not only will he avoid killing his enemies, if his enemies are dying of natural causes or of a HoistByTheirOwnPetard situation, [[UpToEleven if he can, he'll save them]], even villains as bad as ComicBook/TheJoker.
** This is the basis of [[ComicBook/{{Azrael}} Jean-Paul Valley]]'s tenure as Batman during ''[[ComicBook/{{Knightfall}} Knightquest]]'' as he would be lost within the System and constantly battling between acting like Batman and acting like Azrael. It's only when he allows Abattoir to die that everyone decides to shut him down.
** During [[https://www.youtube.com/watch?v=wAg2m5UlBYw a non-canon fight]] between Batman and ComicBook/{{Deadpool}}, Deadpool mocks that Batman can't beat him because he can't be killed. Batman snaps, "I'm ''counting'' on that." Cue Batmobile twin rocket launchers turning Deadpool into LudicrousGibs. After Bats leaves with Catwoman, Deadpool's head is mildly annoyed, chiefly because he has the munchies and Bats left before he could ask him to buy him chimichangas as consolation.
** In fact, Batman hates to see ''anyone'' die. It's the crux of ''ComicBook/KingdomCome'' when Superman tells him the one thing they both had in common was they saved people. Heck, in ''ComicBook/JLAAvengers'', while Plastic Man is amused by ComicBook/ThePunisher killing drug dealers in a firefight, Batman immediately goes to beat the everliving crap out of Frank, to ''save'' said dealers.
** Batman's rule sometimes goes into StupidGood territory, like in a ''ComicBook/JudgeDredd'' crossover when he expressed sorrow for (seemingly) destroying the zombified monster Judge Death. Dredd has to remind him that they're not even alive to begin with.
*** He's similarly called out on this in ''WesternAnimation/BatmanUnderTheRedHood'', in which [[spoiler: Jason Todd asks "Why, on God's green earth, is ''[[ComicBook/TheJoker he]]'' still alive?!"]]
** This was deconstructed in ''ComicBook/DetectiveComicsRebirth''. [[spoiler:To wit, Batwoman is forced to kill Clayface to save Cassandra Cain and Batman is furious. He calls in Dick, Jason, Tim, Damian, and Barbara to discuss this and possible punishments. While Dick and Tim side with Bruce, Jason and Barbara side with Kate. Jason accuses Bruce of playing to a double standard, though Barbara claims Bruce is scared of losing Kate as Kate is his last connection to his mother, Martha. Even more damning, he's afraid that if Martha knew of this, she would have sided with Kate, effectively killing any argument for his rule.]]
** Batman's crossovers with ''Franchise/{{Predator}}'' and ''Franchise/{{Alien}}'' zig-zag this. In the ''Predator'' crossovers, Batman refused to kill the alien hunters despite them trying to kill him. This is mostly because they are intelligent and have a code of honor which he tries to use to his advantage. In the ''Alien'' crossovers, he's more than likely to kill them since they're animalistic.
** Out of the ComicBook/{{Robin}}s:
*** [[ComicBook/{{Nightwing}} Dick Grayson]] (Robin I/Nightwing) followed this rule to a T during his tenure as Robin and as Nightwing [[spoiler: is normally a firm believer and follower of this rule, however he ''did'' beat the Joker to death in rage when taunted about [[KnightTemplarBigBrother Robin's death]] ([[JokerImmunity he was revived immediately]])]].
*** Jason Todd (Robin II/Red Hood) kept to this rule save for one ambiguous interaction with a rapist who fell to his death until he returned from the [[CameBackWrong dead]] and very much subverted it.
*** [[ComicBook/RobinSeries Tim Drake]] (Robin III/Red Robin) has followed his mentor's rule, [[spoiler: though at one point he set up a test for himself to see if he would kill his father's murderer by setting up a death trap for Captain Boomerang; in the end, he saved him]].
*** In ''ComicBook/{{Knightfall}}'', Tim remains shaken by Abbatoir's death, saying he would never forget how he died in front of him thanks to Jean-Paul. Bruce approves sadly, telling him to ''never'' forget that feeling. Once he loses that feeling, he will have lost some part of his humanity.
*** [[ComicBook/Batgirl2009 Stephanie Brown]] (Spoiler/Batgirl IV) had trouble with this rule when she first started out as Spoiler but Tim Drake and her experiences as a crimefighter convinced her early on to adopt Batman's no killing policy.
*** [[ComicBook/RobinSonOfBatman Damian Wayne]] (Robin V) was raised as a killer before he met his father and has some trouble with this rule initially during his tenure as Robin.
* ''ComicBook/BirdsOfPrey'' member ComicBook/{{Huntress}} had no time for this early in her vigilante career. She's getting better, but she still doesn't seem to have too much of a problem with killing criminals. It's the main reason Franchise/{{Batman}} doesn't trust her. Oracle, being more forgiving and willing to offer second chances, does trust her. Oracle does, however, use this excuse to treat her like crap.