Many heroes walk a thin line between good and evil; indeed, many heroes have fallen into despair, rage or even madness, and once proud heroes descend further into the path of evil, often fighting against people they once protected or fought alongside.

Originally protagonists or forces of good, these villains turn evil due to events in their lives, such as being corrupted by another villain (i.e. convinced by villain's arguments), their desire for revenge, a failed love relationship, betrayal from the good side to the dark side, or any other unresolved traumatic experience in which they question whether or not the good side is worth fighting for.

A Fallen Hero - or hero turned to the dark side - is usually the end result of a protagonist exposed to a Corrupting Influence, Deal Makers, Brainwasher, and occasionally an Extortionist, Blackmailers, or even Bond Destroyers. However, some heroes may turn for more greedy reasons (i.e. "From Sugar to Excrement" scenario).

In the worst cases, some heroes turned to the dark side can become Purely Evil to add drama as they are willing to be evil without any remorse or positive qualities after all. However, some of them can still redeem themselves, especially if they were former henchmen who eventually betrayed their masters when they come to realize just how evil they really are (e. g. Alphus).

There are various scenarios for why these individuals turned to the dark side, though the said individual often to fell onto multiple scenarios altogether:

• 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 about this. 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 who was often abused by other people that dislike/hate them (either the Big Bad or merely minor villains in the story) 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. Nightmare Sans is a good example of this.
  • 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. Not because they are Complete Monsters, but because they almost never forgive or forget, and/or are now completely insane and cannot be reasoned with. Often, they enact the exact same cruelty, or even worse cruelty, on their tormentors, and even innocent people, making them no different or even worse than their tormentors. Jeff the Killer is a good example of this.
• Not good with Rejection: A character may have once had an acquaintance or love interest who befriended them prior to their turn to the dark side. One day, the individual either made an offer, confessed their love, or presented a certain proposal to the hero(es) which the hero(es) rejected. The individual, unable to cope with this, turned to the dark side. Generally, the worse the hero(es) reject(s) the individual, the farther that individual turns to the dark side. Mephiles the Dark is a good example of this.
• 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 most of these characters become Anti-Villains in the process. Exetior and Toad are good examples of this.
• From Sugar to Excrement: These characters were once highly revered and loved by their peers but turned evil, either by greed, lust, or simply because they were "tired" of being good, bringing shock and despair to those who knew them. The Coca-Cola Company is a good example of this.
  • From Defender of life to Power-Hungry: In this sub-scenario, these heroes originally wanted to protect the lives of their people but eventually come to realize that they can use their powers to destroy anything to get more power than before. Nekrozoth is a good example of this.
• 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. Sonic.exe is a good example of this, depending on what version of the story is being used.

Notes[]

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

• Pure of Heart heroes can't turn evil and become fallen heroes because they're completely immune to corruption. If some heroes were considered to be Pure of Heart but eventually turn evil, it means that they were never Pure of Heart in the first place. Therefore, they can never count unless they became villains through mind-control.
• Morally neutral characters (a la "average Joes") or characters initially uninvolved with any side of the conflict do not count (e.g. Francis, Oscar). They should go under From Nobody to Nightmare instead.
• Characters who have been implied to have been heroic in the past (e.g. Professor Brezhnev) also do not count, as while they could have been heroic or have committed heroic actions, there is no in-universe evidence of such.
• False heroes, if they never were good, they do not count either (e.g. Sir Topham Hatt, Robert, Jschlatt and Does Bad Things Guy). They should go under Faux Affably Evil, Liars and/or Hidden Villains instead. However, some false heroes still can be originally heroes no matter how two-faced they are (e.g. Asriel Dreemurr, Wilbur Soot, Tabi and the Funky Fource).
• Normal officials such as businesspeople, CEOs, managers, doctors, scientists, politicians, school faculty, etc. (e.g. Jules Archibald), they should go under Corrupt Officials, Businessmen, and/or Doctors and Scientists instead, unless they did truly heroic deeds with their job in the past.
• Normal public servants such as law enforcement, military, fire department, security, healthcare professionals, etc. who became evil do not count. They should go under Corrupt Officials, Military, Gaolers, and/or Jingoist instead, unless they had heroic motivations for being public servants.
• Young and naïve children who became evil do not count. They should go under Juvenile Delinquents instead, unless they are reported to have done something truly heroic
• Villains who simply lose all of their redeeming qualities do not count, they should go under Debased instead, unless they actually were heroes in the past (e.g. Shadow Ahriman and Dream).
• Servants/Pawns, villains who served on the hero's side but have never done anything heroic do not count either (e.g. Francis). They should go under Servant of Hero instead, unless they actually did genuine heroism.
• Anti-Villains/Protective, Villains who do have noble and/or caring qualities but were not heroes to begin with (e.g. 3650) do not count. 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.
• Nice people, villains that were simply nice people before they became villains (e.g Ominous) also do not count , if they never did anything heroic before they became villains. They should go under Affably Evil instead, unless they have lost their genuine affability, in which they'd fall under Faux Affably Evil or Equally Hostile instead.
• Brainwashed or Forced into it, if a villain was forced into it by circumstance or was brainwashed into becoming heroes, they also do not qualify, a fallen hero must have been a genuine hero before becoming evil.
• Famous people, villains that simply had a good reputation do not count. They should go under Charismatic‏ or Villains with Good Publicity instead, unless their good reputation was earned from heroic deeds in the past.
• Protagonists, villains who are simply the main character in the story do not count either. They should go under Protagonists instead, the villain must be a real hero in order to qualify (e.g. Mario) or formerly were actual heroes before falling into the Dark Side.

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 of Heart 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" 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. Mario).