Ant-Man: Played with concerning Hank Pym. Initially presented as a Nice Guy scientist, he had a number of Jerkass moments when he became Ant-Man, particularly his tendency to dismiss and verbally put down his love interest The Wasp. However, he really took a level when he had a mental breakdown and became the anti-heroic Yellowjacket, eventually getting to the point he tried to cause a robot attack he could foil to look heroic. After hitting rock bottom, he built up and became a Nice Guy again after some development.
Captain America: During Civil War Captain America himself took a level in jackassery, calling Tony a “pampered punk” and generally being an obstinate and violent stick in the mud whom refuses to listen to the other side of the argument. The writer Mark Millar is the one created the infamously douchey Ultimate Cap and it’s abundantly clear his interpretation bleed over onto main universe Steve.
Cap got this again in Avengers vs. X-Men where his usual genteel diplomacy is thrown out the window as he hounds Hope Summers demanding she be handed over and ignoring the mutants’ protests acting like an asshole General Ripper rather than The Paragon.
Worth noting there’s some Revisiting the Roots at play here as Cap similar to Superman actually Took a Level in Kindness from the 1940s comics to his reintroduction in the 60s. Classic Cap was a hotheaded vigilante who insulted his enemies and had quite a mean streak (he routinely disrespected and humiliated Sargent Duffy, just because) it was only when Stan Lee and Jack Kirby brought him back that Steve was written to be the idealistic incorruptible figure most fans know.
Captain Marvel: A lot of people note Carol Danvers received this upon discarding her Ms. Marvel persona and becoming the new Captain Marvel. While she’s always been abrasive and outspoken and in at least one comic happy to let an alien villain suffocate in the vacuum space in front of her, she was still generally compassionate, patient and unambiguously heroic. The moments where she lashed out at people were usually justified Example The What the Hell, Hero? she gives the Avengers who were largely unconcerned about the whole “mystically impregnated under mind control by her own Timey-Wimey Ball son Marcus” thing or at least sympathetic given her bouts with alcoholism and a domineering misogynistic father who ignored her achievements and wanted her to Stay in the Kitchen. After becoming Captain Marvel however her nicer moments soon became fewer and far between as Carol started getting written more like a superpowered Maria Hill being extremely callous, suspicious, short tempered and tactless. This cumulated in Civil War II where Carol is essentially a Villain Protagonist who uses Ulysses to hound people down, gets Rhodey, She-Hulk and Bruce Banner killed and puts Tony in a coma. Tellingly even Kamala (her protégé amd greatest fan) disowned Carol for her actions and sided against her. Much like Tony though she does become nice again in the wake of her actions and becomes The Atoner, acknowledging she has problems that need fixing.
Ironically the same process happened in reverse for Carol’s rival Rogue who started off as a butch, short-haired, arrogant Hate Sink but eventually became a more compassionate and heroic person. This case of Swapped Roles is partially acknowledged In-Universe however, leading to one truly heartwarming moment in Captain Marvel (2019) Issue #49 where Rogue is the one to talk Carol back from her Despair Event Horizon saying neither of them are Beyond Redemption for their actions and she won’t let Carol carry her burdens alone. They hug.
Nearly every incarnation of the Hulk goes through periods where he goes from Woobie to Jerkass Woobie to just plain Jerkass. Then again, it's The Hulk. His different personalities have different levels of jerkass. The most notable one was his Grey Hulk phase, or Mr. Fixit as he called himself. This Hulk enjoyed beating people a bit too much and even accepted to work as an enforcer in Vegas so he could earn money for punching people all day. His newfound intelligence allowed him to be much crueler with his foes than the classic Green Hulk ever was. For example, when attacked by the Rock and Redeemer, he took advantage of the Rock's spinning spikes attack, smashing Redeemer against said spikes and effectively killing him. In Immortal Hulk however Joe actually Took a Level in Kindness and decides to be a hero again.
Bruce himself has gotten this in the modern era. Originally he was a pure Nice Guy and The Woobie but in the 2000s Bruce is written to be more of a self-destructive nihilist who wants nothing more than to destroy his child-like alter ego and alienates practically everyone who loves and cares about him including his wife Betty and cousin Jennifer. The cumulates in the 2011 series where it’s explicitly stated and shown without Hulk to vent his impulses Bruce would be a Mad Scientist. Not helping this is an earlier retcon flashback storyline that reveals Bruce almost blew up his high school to get revenge on his bullies. In Immortal Hulk however Bruce is written to be more of a Knight in Sour Armour who is a good person deep down and manages to comes to terms with his personas. Sadly this was development was ignored when Donny Cates took over from Al Ewing.
Betty Ross has gotten this ever since The Reveal that Red She-Hulk is her. Previously she was a compassionate and loving person whom cared deeply for Bruce as his wife, the only times where she was violent or cruel was when she was Harpy. Since her Red She-Hulk revamp she’s been written to be cold, vindictive and angry especially to Bruce whom she lashes out against frequently. Although this attitude is pretty damn justified if you consider the Trauma Conga Line Betty has been through i.e getting turned into a monster, her father storming her wedding with a gun, suffering a miscarriage after learning Bruce had been killed, getting gamma radiation poisoning, being mystically raped and impregnated by Nightmare (Depending on the Writer whether it was her or some other woman) and has been cheated on twice when Hulk slept with two alien women, one of whom Caiera gave birth to two sons. Can you really fault her for being callous after all that?
General Thaddeus “Thunderbolt” Ross believe it or not got this as well. While he was always kinda a prick, Ross in the Silver Age was really closer to J.Jonah Jameson; an annoying pain in the ass and antagonistic force for the hero yes but nothing worse and similar to Jonah his redeeming traits (his love for Betty) were empathised and he generally was much less of a threat than the Monster of the Week. This eventually changed with Ross becoming more and more of a monster after learning Bruce was Hulk who was disowned even by his daughter and became a villainous Hulk himself as Red Hulk. He slightly improves when he becomes an Anti-Hero but still doubtless The Friend Nobody Likes.
Iron Man: Although Iron Man was already somewhat of a jerk, during the Civil War/Secret Invasion period he was borderline approaching villain status. Thankfully, the movie helped him to get the better of it.
He got worse again during the "Superior Iron Man" phase, though this was due to his alignment being inverted during AXIS.
The Punisher: Detective Molly von Richthofen was a Jerk with a Heart of Gold at worst when she first appeared in The Punisher: Welcome Back, Frank, being the only character to not completely treat Detective Soap horribly despite being annoyed by his whining. When she returned in the arc "The Resurrection of Ma Gnucci" in Punisher War Zone 8 years later, she's now an insanely jealous Psycho LesbianYandere who brutally attacks and beats anyone who even looks the wrong way at her bisexual partner. When she ends up getting suspended and her partner later breaks up with her (surprisingly, not for any of the unprovoked beatings she delivered), when she comes across a punk who's traded barbs with her in the past, she takes things out on him by shooting and killing his dog when it pees on the street.
In his earlier appearances, Curt Connors was a reasonably sympathetic character when he wasn't the Lizard, and even as the Lizard retained some protective instincts towards his family. He was retconned into being Evil All Along, and as of The Gauntlet he completely lost control of the Lizard persona and killed and ate his own son. After that, his more sympathetic characterization likely won't be coming back any time soon… until Nick Spencer’s run where he’s depicted as a Science Hero. It helps that his son’s death was undone by Jackal.
The Evil All Along ret-con was pretty much ret-conned itself after the story that introduced the idea, as no other writer has used it since then.
In The Spectacular Spider-Man, The Venom symbiote is shown emotionally, psychologically, and physically torturing Eddie Brock in order to milk every last drop of adrenaline from his body, intending to leave him for dead to find a healthy host—preferably Spider-Man—after his terminal cancer made a comeback.
Sub-Mariner: Namor, with his oxygen-processing problem, is either an arrogant but noble superhero or The Friend Nobody Likes. Granted he’s always been kind of a dick who dislikes and attacks humanity even as early as 1939.
Nightcrawler started as a nice guy, as the mainstream version. Then he had an homophobic reaction when Colossus came out of the closet, and then towards all the X-Men.
Initially, Pyro helped other mutants and even joined the X-Men. Then came The Ultimates 3, where he was not only turned into a villain for no real reason, but suggested he and Mastermind rape Valkyrie.
Cyclops has suffered this for decades to the point where it’s become Flanderization, he’s never been as popular as other X-Men (especially Wolverine and Storm) despite being The Leader so writers have no problem dragging poor Scott through the dirt and making him look as bad as possible. While Cyke wasn’t the most cuddle and warm person to begin with — his aloofness was explicitly called out and jabbed at by Iceman, Beast and Angel from the earliest comics, he was still The Cape being just as much a boy scout as Captain America. Overtime Cyclops started getting written to be more and more of a jerk with him infamously leaving his pregnant wife Madelyne Pryor to be with Jean Grey after she was Back from the Dead (before Maddy was retconned to be Jean’s clone). Scott only got worse after Scott married Jean as not only did he start to have mental affairs with Emma Frost but also uses X-Force as his personal wet works kill-squad and gets over Jean’s second death way too quickly to shack up with Emma (another retcon explains Jean wanted Scott to happy and changed reality to make it happen). This all cumulated in Scott becoming a Fallen Hero after the Avengers vs. X-Men business and likened to a mutant Hitler. Fortunately for Cyclops’ fans this was eventually undone with Scott becoming a hero again in X-Men (2019) though he still remains as troubled as ever.
Most of the New Mutants, but especially Cannonball, who went from Nice Guy to aggressive jerk. This was gradually fixed, however.
A New X-Men example with Hellion. While already a tremendous ass to begin with, he somehow still managed to take another level after his hands got blown off by Bastion.
Believe it or not but Mystique got this. While still a villain under her creator Chris Claremont’s pen Raven was consistently a Noble Demon who showed a fair number of standards (she didn’t kill Charles when he was at her mercy) and sympathetic qualities (she genuinely cherished Rogue and stayed her hand when about to stab Nightcrawler, her son). After Claremont left, it became de rigueur for writers to make Mystique as the biggest blue bitch on the planet with her disgustingly abusing and hurting Rogue on the regular and her cruelty went from moderate to Kick the Dog obscene. For example, she killed her son Graydon whom she abandoned and spurned with zero hesitation or so much as a single twinge of regret. She doesn’t get any better in X-Men (2019) with Raven eventually betraying everyone again to bring Destiny back though granted Moira was keeping Destiny dead so she wouldn’t spill beans about The Plan to end mutantkind, so Mystique was the Lesser of Two Evils there.
Kitty Pryde: After Teen Scott leaves in All-New X-Men, she acts like a jerk to Modern Scott and says she doesn't want Scott and Teen Jean alone, since Teen Jean showed some attraction to Scott... even though she admits that Scott handled the situation well. Then, she berates Teen Angel for letting X-23 leave, even though there's nothing he could've done outside knocking her out, which he probably couldn't even have done. As she berates Teen Angel, she half admits that the reason for her shift in attitude, temporary as it is, is that she's trying to keep her students safe and feels like she's losing control. In X-Men (2019) Kitty (now Kate) walks the fine line between the righteous person she usually is and a more wild and brutal anti-hero as the new Red Queen and Pirate Girl of the Hellfire Club in Marauders (2022) — which is probably inevitable when you team up with the likes of Emma Frost, Daken and Kwannon.
Illyana Rasputin used to be a sweet, innocent kid until she was kidnapped by a demon. After spending one decade forced to live among demons and learn dark magic, she often acts as an abrasive asshole. In Avengers vs. X-Men, she started imprisoning captured Avengers by having demons feed on their souls until they were comatose.
Beast's days of being friendly and lovable seem to be behind him. Starting after M-Day, he began making more and more morally questionable choices thinking only he could be trusted to make the right call. By the Krakoan Age he's become a villain in all but name. He's mind-controlled the leaders of a foreign country, ran a secret prison to experiment on prisoners, murdered Wolverine, and then secretly mind-controlled him as an assassin. Eventually this got so bad, the writers were forced to have Hank clone himself with the clone being classical Nice Guy Beast after enough fans got upset with the Character Derailment.
Destiny also gets this in the Krakoan Age. Previously she was written to be the nicer mom of Rogue compared to Mystique, being polite, patient, and kind despite still being a villain. In Necrosha◊ when Back from the Dead with Rogue Destiny gave her adoptive daughter a So Proud of You and said she’d love her no matter what. This attitude was thrown in the trash when Destiny came back for real as she’s an emotionally manipulative Control Freak to Rogue same as Mystique and spites her daughter’s marriage to Gambit.
While Beast and Destiny got this bad more recently, neither can really hold a candle to Moira MacTaggert. Thanks to Jonathan Hickman Moira not only retroactively Took a Level in Badass from the gentle and caring Token HumanLove Interest of Charles but also became a toxic, misanthropic, despicable Team Killer who thanks to her retcon Reincarnation mutant power has decided all mutants must die. Her actions after being exposed and De Powered in Inferno only become more and more cartoonishly sadistic with her kidnapping and impersonating Mary Jane Watson to get into the Hellfire Gala, taking a page of Mystique book and being an abusive mother to Proteus again (just because) and even killing Banshee (one of her dearest lovers and friends) in cold blood and stripping his skin for sake of getting into Krakoa. Fans are generally split whether this was a compelling turn for a previously minor character or character assassination of a hero for the sake of a new villain.
Character Derailment.
◊ when Back from the Dead with Rogue Destiny gave her adoptive daughter a So Proud of You and said she’d love her no matter what. This attitude was thrown in the trash when Destiny came back for real as she’s an emotionally manipulative Control Freak to Rogue same as Mystique and spites her daughter’s marriage to Gambit.
