Fallen Hero / Western Animation

• Adventure Time has a few fallen heroes:
  • Simon Petrikov/The Ice King. As a human, he was a scholar, a loving fiance, and a Parental Substitute to a little girl who had been abandoned during the middle of World War 3. But the Ice Crown mentally warped him until he was unable to remember himself at all, leaving the insane husk that Finn and Jake know presently. He later returns to his original self in the series finale "Come Along With Me" thanks to his fiancee Betty Grof however.
  • Marceline The Vampire Queen. She used to dedicate her life to protecting humanity from vampires. However, after being turned into a vampire herself, being forced to abandon her human group, and realizing the ciclical nature of history, she has become too jaded to continue caring about heroics.
  • Later at the end of season 7, Fern is created after the Grass Sword fuses with the Finn Sword and Finn's alternate self and acts as a more violent version of Finn. Throughout Season 8, Fern attempts to find himself and tries to do Finn's job while he is away from Ooo, only to fail when the Elemental wave spread throughout the land. During the last two episodes of the season, the curse of the Grass Sword manages to take control of the alternate Finn and causes Fern to attempt to replace Finn and take over his life. After getting into a brief right Finn accidentally shreds Fern and becomes traumatized by the incident.
• Adventures of the Gummi Bears: Before becoming a villain who wants to take over Dunwyn, Duke Igthorn was one of the knights who defended it.
• A dark version in Avatar: The Last Airbender is Hama, a seemingly nice old woman from the South Water Tribe living in the Fire Nation. In her youth, she was one of the best waterbenders of the tribe and fought unceasingly to protect it from the Fire Nation invaders. After repeated skirmishes to capture the waterbenders, she was the only one of them left in the tribe and ultimately got captured and thrown into prison with the rest, kept away from any water source and left to rot for the rest of her life. While imprisoned, she discovered a simple but revolutionary truth: living things are made of water, and during full moons, she can use the empowered bending to control them. She improved her bending in secret until she was ready to escape and terrorize the people of the nation that made her life hell.
  • Sequel Series The Legend of Korra has Kuvira, the Big Bad of the final season. Originally Suyin's protege who helped save Korra's father, she leaves to attempt to help stabilize and unite the weakened Earth Kingdom following the events of Zaheer's anarchist uprising. Over the next three years, she rose from her position as a city's guard captain to a highly respected and feared public figure. Desiring to keep the Earth Kingdom safe and united, and seeing the monarchy as obsolete, she usurped the Prince and reestablished the Earth Kingdom as the Earth Empire, which she ruled with an iron fist. Once Korra saved her life, she was able to make Kuvira see just how far she'd fallen from her previously noble intentions, convincing her to surrender willingly.
• The Batman: Ethan Bennett is an honest cop and a close friend of Bruce until (already under stress due to an argument with Chief Rojas) he becomes the victim of Mind Rape by the Joker and is then exposed to the villain's Joker Putty, turning him into a clay-like monster. The whole experience drives him mad and turns him into this continuity's version of Clayface, who is more than capable of murder.
• Batman: The Animated Series: Before his transformation into Two-Face, Harvey Dent is a regular character in the show, an ally of Gordon, and Bruce Wayne's closest friend. In the series' final episode, "Judgement Day", Dent becomes an Anti-Villain known as the Judge and actually tries to kill the Penguin, Killer Croc, and various other hardened criminals... including himself (of which his two previous personalities are unaware). Thus, does he (somewhat) gain his redemption.
• In Challenge of the GoBots, Cy-Kill was once one of the High Protectors of Gobotron and Leader-1's best friend.
• Codename: Kids Next Door:
  • The Delightful Children from Down the Lane are recurring antagonists who serve Father. They're formerly the members of Sector Z, but they were captured and delightfulized by Father into what they are today. What makes this tragic is that the delightfulization process was so thorough that they could only break out of it temporarily before reverting back to their brainwashing.
    Delightful Children From Down the Lane: [as they’re reverting back] Tell the Kids Next Door... we miss them.
  • There's also Cree Lincoln, Numbuh Five's sister and once the best operative the KND had, who later became one of their worst enemies. Also counts as a Broken Pedestal and a case of Cain and Abel in Numbuh Five's case.
  • In fact, the KND seems to have a problem with traitors a lot. That may be the whole reason they inflict Laser-Guided Amnesia on operatives when they retire. On a positive note, both Chad and Maurice were Fake Defectors, subversions of this trope, although, in Chad's case, the revelation didn't make Numbuh One like him again.
  • Minor villains Mr. Wink and Mr. Fibb used to be a part of the Cowboy Kids Club, a group similar to the KND. They later grew up to become evil adults.
• Danny Phantom finds this as his future. He did some pretty disturbing things in that future, including murdering his human self along with probably hundreds of others and doing millions in property damages...at least. Quite shocking, given the otherwise childish, campy tone of the series. Danny, upon seeing this, is extremely horrified by his actions.
• In a Bad Future episode of Darkwing Duck, Gosalyn winds up traveling to the future when trying to stop Quackerjack and Megavolt from doing so. Upon arrival, they find out that Darkwing became "Darkwarrior Duck", complete with red eyes, out of grief over Gosalyn having "run away". He became nigh-catatonic until he saw a girl resembling Gosalyn getting her doll stolen, losing his moral compass in the process, to the point that he threatened people for eating unhealthily and dismissing Launchpad when the latter suggested arresting criminals prior to executing them.
• Justice League:
  • The Justice Lords, following the death of their Flash, became Knight Templars and transformed their earth into a metahuman-ruled dystopia where dissidents and supervillains were lobotomized. The Superman quote from the episode "A Better World" is given just before the Superman of this parallel world crosses the line and kills his Lex Luthor, who was responsible for the death of this world's version of The Flash, with his heat-vision:
    "I did love being a hero. But if this is where it leads, I'm done with it."
  • Shayera Hol a.k.a. Hawkgirl is considered this after it's discovered that she's The Mole during the Thanagarian invasion in "Starcrossed", which causes her to leave the League, though Alfred begs to differ. However, upon rejoining the Justice League, she becomes a hero again, but discards the name "Hawkgirl" due to the lies, disgrace, and treachery that the name carries. Therefore, as of Unlimited, Shayera considers her alter ego to be a fallen hero.
• Shego in Kim Possible, according to her backstory. She was part of the superhero family "Team Go" alongside her brothers, but she became annoyed with her brothers' quirks and left, becoming a supervillainess. However, it's implied there's more to the picture since their parents are absent and Shego was hostile with her brothers even back then.
• Alpha from Men in Black: The Series was the first head of the organization and mentored K, but then power got into his head and he went rogue.
• My Little Pony: Friendship Is Magic: Princess Luna, the very first villain of the series, is an Alicorn goddess who, alongside her older sister Celestia, once co-ruled Equestria, managed the day-night cycle and fought to defeat the Mad God Discord and the tyrannical King Sombra. A combination of perceived ingratitude on the part of her subjects and a vaguely-defined dark force corrupted her into the vengeful "Nightmare Moon", and Celestia was forced to seal her away in the moon to prevent her from bringing about global extinction through The Night That Never Ends, but when she escapes, she's ultimately redeemed rather than killed. The second season's Halloween Episode focuses on her attempts to atone — it's difficult to be accepted as good when you represent The Sacred Darkness in a society which you yourself helped to convince that Dark Is Evil.
• OK K.O.! Let's Be Heroes: Professor Venomous is revealed to be one in the episode "Big Reveal". Back when he was the hero Laserblast, he was a vital member of his team and had a loving and supporting girlfriend, but suffered from crippling self-esteem issues in regards to his powers, which he felt were unimpressive compared to those of his teammates. He took to experimenting in secret in order to improve them, but his lab was discovered by Greyman, and the rest of the team — believing it belonged to an unknown villain — decided to have it destroyed. In what would eventually become known as the Sandwich Incident, he went into the lab first to try and save his works and destroy any links to him, but accidentally caused an explosion that gave him a permanent De-power and made it look like he was dead. To top it off, he heard his girlfriend say something that made it sound like all her support for him had been false, which ultimately caused him to flee the scene in shame, not wanting to face her or his teammates. Over the years, he tried to get his powers back with no success; however, he did end up finding great success in marketing to villains, turning him into the Card-Carrying Villain he is in the present.
• Rick and Morty: Implied to be what happened to Rick Sanchez in the past. When talking to Beth (or a clone of Beth?), Rick states that he had a 'hero phase' that he grew out of.
• South Park
  • Heidi Turner, who was one of the leading heroic characters in Season 20, becomes Eric Cartman's Distaff Counterpart by the next season, with all her kindness turning into complete jerkassery.
  • Mr. Hankey manage fall even further going from the boys' occasional savior to a self-destructive asshole by Season 22. At least Heidi was able to realize how far she fell before reverting back to her old self. Mr. Hankey on the other hand outright refuses to acknowledge fault for his own actions blaming his obnoxious behavior on Ambient leading to the townsfolk to force him out of South Park.
  • Randy Marsh managed to fall even worse than the above. In Season 22, he started off as a noble owner of a small weed business who stood up and fought against corrupt businesses. However, by Season 23, the success of his weed business turned Randy into a Corrupt Corporate Executive committing amoral acts, such as blowing up people's homes and killing Winnie the Pooh, to keep his business afloat. Luckily Randy does get a Heel Realization after getting arrested in "Season Finale".
• Over the course of Star Wars: The Clone Wars, Barriss Offee turns into this, due to being increasingly embitered on how corrupted the Jedi Order has turned in the last few years, and leads her to fall into The Dark Side. It culminates on her doing a bombing on the Jedi Temple's hangar that she frames Ahsoka Tano for, and while she's discovered and arrested, her actions ultimately plant the seed that leads to the fall of the Jedi Order as a whole. Ironically, Barriss failed to realize that she was doing exactly what she accused the Jedi Order of: falling to the Dark Side without even realizing it, then becoming too corrupted to be capable of realizing it.
• Storm Hawks
  • The Dark Ace of the Cyclonian Empire was once a member of the original Storm Hawks, the greatest team of Sky Knights in all of Atmos, and the co-pilot of the leader, Lightning Strike. They fought to free Atmos of the terror of Cyclonia and united the free people of Atmos against them in what was to be their greatest triumph. However, tempted by the offer of power and glory from the previous Master Cyclonis, the Dark Ace betrayed his fellows and personally struck down Lightning Strike, allowing Cyclonia to win and him to reap the rewards of his betrayal. By the present day, the Dark Ace is now the most dangerous member of the Cyclonian army and The Dragon to the current Master Cyclonis in her bid to conquer all of Atmos, a station he holds with pride.
  • Carver was once the leader of the Red Eagles, considered the greatest Sky Knight squadron since the original Storm Hawks, and a national hero with legions of fans. He was so respected that his team had the honor of being the guardians of Terra Atmosia, the bureaucratic center of the free terras and home base of the Sky Knight Council and the powerful Aurora Stone. However, like the Dark Ace before him, Carver became tempted by the power of the Cyclonian Empire and betrayed his fellows to steal the Aurora Stone to give it to Master Cyclonis, only to be barely stopped by Aerrow and imprisoned. In "Second Chances", he gets a chance to redeem himself when evidence becomes uncovered that he was actually under mind-control and joins the Storm Hawks to help them become better heroes and celebrities only for it to turn out that not only was he Not Brainwashed, he's been trying to kill Aerrow out of revenge for his previous defeat, squandering the faith the people had in him and being thrown back in jail.
• Super Robot Monkey Team Hyperforce Go! has Mandarin. Once, he was the leader of the team but was consumed with a desire to rule those weaker than him, eventually driving him to become The Dragon to the Skeleton King.
• Teen Titans (2003) had Terra, who started off as a good-natured girl with unstable powers, but was eventually drawn to becoming Slade's apprentice in exchange for him teaching her to control her powers, leading to her betrayal and becoming a villain.
• One of the villains in the Teenage Mutant Ninja Turtles (2012) Elseworld three-parter "Raphael: Mutant Apocalypse" sees one of the Bad Future's warlords, Maximus Kong, be revealed to be an even further mutated Leonardo.
• Transformers:
  • Transformers: Animated:
    • Blackarachnia. Getting abandoned on a hostile planet and suffering nasty Body Horror involving a Giant Spider or twenty would make anyone a little bitter.
    • Wasp, who, after being falsely accused of being a traitor, spends over 50 years in prison and goes insane. Poor guy. He's a Darker and Edgier take on the Beast Wars comic relief character, talking normally in flashbacks but more like his past counterpart in the present as Sanity Slippage has fully taken hold. When he is altered to fully become Waspinator, he's a massive, powerful, unkillable engine of revenge. However, that's not to say that he was a decent guy before. As Bulkhead put it, "You may not have been a traitor, but you were never a good bot."
  • Wheeljack from Transformers: Armada. After believing that Hot Shot abandoned him and left him for dead, he does a Face–Heel Turn and joins the Decepticons. He comes back for revenge.
  • An earlier one: Rhinox from Beast Wars becoming Tankor of Beast Machines.
  • Depthcharge was apparently a model Maximal before Rampage wiped out Colony Omicron, turning him into a grim and obsessed hunter.
  • And Megatronus Prime, the thirteenth original Transformer. You should know him as the Fallen, with his original name being taken by Megatron, who in most continuities idolized him enough to take his name.
  • Megatron himself generally follows this in most continuities this side of the IDW comics expanding his backstory. What usually happens is, at first, the Autobot regime is corrupt and dictatorial, and Megatron rebels against that, being a genuinely heroic revolutionary fighting for social change (often for the sake of a highly oppressed working class). Indeed, he often starts off as a member of one of the lowest working classes such as a miner or gladiator. Then right around the time he actually manages to get rid of the 'bots responsible to the point where the Autobots have enacted the change he wanted and become a genuinely morally upstanding society, the stress and thrill start driving him to become even eviler and power-hungry than the ones he was fighting, and so the civil war he started continues with the "good" and "evil" labels having switched somewhere along the way.
• Surprisingly and hilariously, VeggieTales parodies the story of David, Uriah, and Bathesheba. David is Larry, Uriah "only" becomes crazy, and Bathesheba... is a rubber duck. That is somehow better than any other rubber duck, and greed for it is why David, instead of minding his own business, sends Uriah away. When Uriah comes back, he's too insane to know his duck is gone.
• W.I.T.C.H. has Nerissa, a former Guardian who was corrupted by power and killed a fellow Guardian, was imprisoned, and returned to become the Big Bad of Season 2.
• Chase Young of Xiaolin Showdown used to be a heroic monk under Grand Master Dashi, until Hannibal Roy Bean convinced him to trade his soul for an immortality potion. Since then, he's been one of the world's greatest evils.
• In Season 2 of Young Justice (2010), after a Time Skip, we have Aqualad, now Black Manta II. The worst part is that he was The Leader in Season 1. The cause of this was blaming the team for his love interest dying and finding out his real father was the supervillain Black Manta. Viewers can only hope for a Heel–Face Turn.
  • Later revealed that he didn't really go to the dark side. He's The Mole and Dick, Wally, and Artemis are in on The Plan.
    • However Aquagirl really did die, and he really was genuinely devastated by the reveal of his true parentage, to the point where Wally isn't totally confident Aqualad won't end up becoming this for real in the end after all, especially since he's growing a genuine bond with his father, while becoming more and more detached from the team.
    • "Before the Dawn" reveals that Blue Beetle II, Jaime Reyes, becomes this in Bart Allen's future and apparently plays a key role in initiating the apocalypse — Jaime is the main reason Bart traveled to the past in the first place.