Heroes walk a thin line between good and evil and many once-proud heroes have fallen into negativity or descended further into darkness fighting against people they once protected and/or fought alongside. Some end up becoming even worse than those they opposed.

Originally protagonists or forces of good, these villains turned evil due to events in their lives such as being corrupted by other villains, relationships, or any in which they question whether or not the good side is worth fighting for. Sometimes, they betray their friends, family, or even country out of cowardice.

Fallen Heroes or Heroes Turned to the Dark Side are usually the end result of being Betrayed, Vengeful, Tragic, In Love, exposed to Corrupting Influences, Deal Makers, Brainwashers, Extortionists, Blackmailers, and/or Bond Destroyers (i.e. Kayako Saeki, Sadako Yamamura, and Esther Coleman). However, some heroes can turn for the sake of greed (i.e. "From Sugar to Excrement").

Some can still redeem themselves, especially if they were Minions who turned on their masters or themselves after realizing how evil they were or in order to save a loved one (i.e. Darth Vader, Kylo Ren, Cassandra, and Alberto Alburquerque). Villains who were mind-controlled can count as this if they were good before being controlled or in rare cases, fake being mind-controlled to get away with their crimes.

There are various scenarios for why these individuals turned to the dark side, though said individuals often fall into multiple scenarios:

• From Zero to Nightmare: A scenario where the said hero turned to the dark side in this way often became a shocking event for either viewer, heroes or other people that found out. Reason of this mainly because the said hero was always looked down upon, his/her existence was ignored, and/or worse, considered as an outcast or an individual that often being abused by other people that dislike/hate them (either the Big Bads or minor villains) no matter what kind of good/heroic efforts that he/she did for others' acknowledgement. Once this individual turned to the dark side, they (usually) became feared by many people, including heroes that faced them. Good examples of this include Savitar, Dave, and various incarnations of Frankenstein's Monster.
  • From Victim to Villain: In this sub-scenario, these characters were once people who tried to be friendly and do good, but were rewarded with injustice and ingratitude by society. Often, they were victims of bullying or abuse and eventually, they were pushed so hard they finally snapped and now seek revenge on the very society or people that shunned and hated them. Despite their tragic nature, very few of these characters actually are redeemable, mostly because they almost never forgive or forget and/or are now completely insane and cannot be reasoned with. They enact the same or even worse cruelties on tormentors and even innocents making them no different or worse than them (i.e. Lucy and Andrew Detmer). Furthermore, they often use their tragic upbringing to excuse the nature of their crimes which makes them less sympathetic if their actions outweigh any injustices they experienced.
• Not Good with Rejection: The character may have once had acquaintances or love interests who befriended them prior. One day the individuals made an offer, confessed their love and/or presented a certain proposal to the hero(es) which the hero(es) rejected. The individual, unable to cope and thus turned to the dark side. Generally, the worse the hero(es) rejects the individual, the farther that individual turns to the dark side (i.e. Bill and Maker).
• Being an Extremist: A character has well-intentioned goals for the greater good, but their methods and ultimate ends are proven to be very extreme to the point that they become something that is greatly despised, whether by those whom they know, the heroes, or themselves. The said actions may even potentially drive them to the dark side as well even if they become Anti-Villains (i.e. Nathaniel Barnes, Mustache Girl, Renegade Shepard, and Damon Gant). However, some of them who were once extremists can go so far in their actions that their "well-intentions" end up being nothing more than just self-serving delusions (i.e. Light Yagami, Zamasu, and Darth Vader).
• From Sugar to Excrement: These characters were once revered but turned evil either by greed, lust or because they were "tired" of being good bringing shock and despair to those who knew them (i.e. Baron Kelvin, Tankor, and Yoshihito Kanamori).
  • From Defender of Life to Power-Hungry: In this sub-scenario, these heroes wanted to protect others but eventually realized that they can use their powers to get more (i.e. Sunset Shimmer, Ultraman Belial, and Elgen Inc.).
• Being Possessed/Brainwashed: Once heroic, these characters were either possessed or brainwashed by another villain or corruptive presence and consequently became villains. However, this is the rarest and most controversial form of a hero turning to the dark side since they did not turn evil by their own free will and essentially had to be programmed into being villainous. Examples may include most of the characters from the Possessed/Brainwashed category. Most of these characters redeem themselves after snapping out of their current state. Another example was Angor Rot from Trollhunters, who was a hero to troll-kind and tried to help people who are unsafe in Gunmar’s war, only to be brainwashed by Gunmar’s indirect creator, Morgana into being evil when he asked her power to protect his village. By the series finale, Angor redeems himself after he realizes whom he was and how evil and cruel he once was.
• Desperation: These characters were people who, despite having followed the rules of life and following their principles, are even affected by the crisis both socially and economically and puts them in danger of putting their daily lives or the things they have managed to maintain during years (a company, for example) to ruin; this causes these characters to fall into (irrational) despair, in order to prolong, or even to "eradicate" the inevitable, forcing them to break the rules and act immorally, whether stealing things (such as money obviously), kidnapping, or even killing the people who persecute them, either for economic reasons, or because they witness their crimes. A good example includes Henry J. Waternoose III, he was only driven to villainy out of desperation to keep Monsters, Inc. afloat in the midst of the energy crisis, as well as due to stressful financial problems and his responsibilities as CEO. Mr. Waternoose became more villainous and manipulative, as this drive and desperation stripped away his morals and was determined to not let anything stop what he believed would be the best way for the company to keep going, never bothering to look for alternative energy sources. He even turned on his most loyal employee to ensure that his plans work out.

Notes

Please note that a character has to have been established as a hero before turning evil.

• Pure Good heroes can't turn evil and become fallen heroes because they're completely immune to corruption. If some heroes were considered to be Pure Good but eventually turn evil, it means that they were never Purely Good in the first place since Pure Good heroes are incorruptable. Therefore, they can never count unless they became villains through mind-control (e.g. Jack-Aku).
• Morally neutral characters (a la "average joes") or characters initially un-involved with any side of the conflict do not count (e.g. Lots-o'-Huggin' Bear, Vellian Crowler, Ren Krawler, Ryuga, Plankton, Cecil Clayton, Syndrome, Freddy Krueger, Lord Shen, Henry Evans, Venom, Joker, Tighten, Jerry Rassic, Lord Voldemort, Penguin, Victor Vega, Zira, Tom Cooper, Lucas Baker, Doctor Doom, Norman Osborn, Joker (2019), Turbo, Andy Evans, Porky Minch, Mami Nanami, The Crusader, and Randall Boggs). They should go under Charismatic and/or Friend of a Hero instead. Some such as the former can, however, can still become purely evil.
• False heroes, if they never were good, they do not count either (e.g. Kristoph Gavin, Emperor Palpatine, Albert Wesker, Napoleon, Mysterio, Grimmel the Grisly, Black Noir, Prince Hans, Carter J. Burke, Scar, Ganondorf, Steele, Judge Claude Frollo, Dawn Bellwether, Ernesto de la Cruz, Edwin, King Runeard, William Afton, Sir Miles Axlerod, Gilderoy Lockhart, Dr. Robotnik, Piella Bakewell, Bill Cipher, Shiranami, Gaku Yashiro, Dimitri Rascalov, Leo Kasper, Tord, Vincent and Zoom). They should go under Faux Affably Evil, Liars, Cheater, Trickster, Hypocrites, Delusional, Traitor, and/or Master Manipulator instead. However, some villains who are false heroes in the present story still can be originally true heroes in the past (e.g. Rex Dangervest, Yokai, Homelander, Namaari, Princess Hilda, Commander Rourke, Peter Pettigrew, Diane Simmons, Harry Flynn, Carl Nesmith, George McHale, Huey Emmerich, Princess Kenny, Saw Gerrera, and Quirinus Quirrell).
• Normal law enforcement, military, fire department, guards, paramedics, agents, wardens, etc who became evil do not count (e.g. Richard Detmer, Howard Payne, Chief McBrusque, Bob Barnes, Bunny, Preston Packard, Major Tint, Alonzo Harris, Norman Stansfield, Frank Tenpenny, Byron Hadley, Schwarlitz Longhener, Godwin Longhener, Agent Trout, Bill Coburn, Samuel Norton, Colonel Muska, Agent Smith and Lord Cutler Beckett). They should go under Corrupt Officials, Military, Gaolers, and/or Jingoists‏‎ instead, unless they are reported to have done something truly heroic (e.g. Bad Cop, Harvey Dent, Ethan Bennit, Commander Cody, Gabriel T. Rorke, General Shepherd, Venom Snake, Fliqpy and Cobra Commander).
• Normal Businessmen/women, CEOs, Managers, workers, doctors, scientists, teachers, mayors, politicians, principals, etc who became evil do not count (e.g Ragyō Kiryūin, Gigayama Tiger, Udo Heinemann, Dr. Pickman, Stromboli, Phineas T. Ratchet, Tortoise John, Director Kakuzawa, Professor Kakuzawa, Samuel Hayden, Yong-suk, Gaku Yashiro, and Dongsoo Seon). They should go under Corrupt Officials, Doctors and Scientists. and/or Businessmen instead, unless they are reported to have done something truly heroic (e.g. Henry J. Waternoose III, Doctor Octopus, Obadiah Stane, Jonathan Irons, Mr. Krabs, The Once-Ler, Severus Snape, Walter Erick Campbell, Jenna Zan Arbor).
• Normal Students, Student council, club presidents, Cheerleaders, etc who became evil do not count (e.g. Andy Evans, Yashiro's Brother, Trina Riffin, Vicky, Shinya Kurai, Buddy Revell, It's a Bully, Chris Hargensen, Amy, Alex, Eric Harris, Dylan Klebold, Vincent the Atheist, Eric, Peter Stegman, Satō Matsuzaka, Gary Smith and Michael Pulaski) They should go under Kids, Teenagers. and/or Juvenile Delinquents, instead, unless they are reported to have done something truly heroic (e.g. Carrie White, Andre Kriegman & Calvin Gabriel and Herman Howards).
• Villains who simply lose all of their redeeming qualities do not count (e.g. Dio Brando, Freddy Krueger, Michael Myers, Joker, Syndrome, Poison Ivy, Ego, Peter Pan, King Zenoheld, Doji, Joker, Frank Underwood, Taurus Bulba (DuckTales 2017), Bradford Buzzard, King Boo, Johan Liebert, Vladimir Makarov, Herrscher of the Void, William Afton, Gelorum, Shiranami, Gaku Yashiro, Owlman, Dimentio, Vilgax, Cinder Fall, Agent Smith, Hans Gruber, Randall Flagg, Frieza and Muzan Kibutsuji), unless they actually were heroes in the past (e.g. Dark Danny, General Mandible, Khan Maykr, Immortan Joe, Commander Rourke, Peter Pettigrew, The Batman Who Laughs, Retak’ka, Light Yagami, Griffith, The Fallen, Grand Moff Tarkin and Koba).
• Servants/Pawns, villains who served on the hero's side but said circumstances have never done anything heroic or good do not count either (e.g. Jafar, Dick Hardly, DOR-15, Allan, Dimentio, Eli Mills, Eramis, Kell of Darkness, and Micah Bell). They should go under Servant of Hero instead, unless they actually did genuine heroism (e.g. Brutaka, AUTO, Lucifer and David 8).
• Anti-Villains/Protective, villains who do have noble and/or caring qualities but were not heroes to begin with do not count (e.g Benjamin Linus, Gus Grav, Volt Luster, Vulture (MCU), and The Puppet) They should go under Anti-Villain, Vigilante, Protective, and/or Extremists instead, unless they actually were heroes who turned to the dark side and still contain their righteous qualities (e.g Kenny, Henry J. Waternoose III, and Billy Butcher).
• Nice people, villains that were simply nice people before they became villains (e.g Isaac Ray Peram Westcott, Dr. Sheridan, Lots-o'-Huggin' Bear, Soon, Dr. Ivo "Eggman" Robotnik, Illyasviel von Einzbern, El Macho, and Herrscher of the Void) also do not count if they did nothing truly heroic before they actually became villains. They should go under Affably Evil instead, unless they have lost their genuine affability.
• Brainwashed or Forced into it, if a villain was forced into it by circumstance or were brainwashed into becoming heroes (e.g Yuuki Terumi), they also do not qualify; a fallen hero must have been a genuine hero before becoming evil (e.g Winter Soldier, Monster Steven, and Boris the Wolf).
• Famous people, villains that simply had good reputation do not count (e.g. Balthazar Bratt, Chester V, Dave, Lionel Starkweather, and Charles F. Muntz), They should go under Charismatic‏ instead, unless they actually were heroes in the past (e.g. Harvey Dent).
• Protagonists, villains who are simply the main character in the story do not count either (e.g. Frank Underwood, Zim, Madea, Stuart, Kevin, and Bob, Minions, and Megamind) They should go under Protagonists instead, the villain must be a real hero in order to qualify (e.g. Jason Brody) or formerly were actual heroes before falling into the Dark Side (eg. Darth Vader and Eren Yeager).

Note that tragic villains do NOT automatically mean that they are heroes turned to the dark side. This category is meant for villains who used to actively work for the good side. Also, this kind of hero is the polar opposite of Pure Good heroes that are absolutely incorruptible.

• Also, do not create pages based on this category, as long time heroes who were only briefly fallen or on and off "jerks" (such as Barnacle Boy, who only fell to the dark side over a Silly Meal and called himself Barnacle Man in the SpongeBob SquarePants episode, Mermaid Man and Barnacle Boy V but then eventually redeemed himself, Luan Loud, who only turns evil in the April Fools episode and does eventually learn her lesson in the end or Mushu, who only was bad when he deliberately tried to put end Mulan and Shang's love to save his career in Mulan 2, but then eventually redeemed himself at the climax of the film) do not count.
  • On the other hand, heroes that are villains in more than several episodes/films can count if they turn evil as time goes on. (e.g. Mitsuzane Kureshima and Varian).