Super-Trope to The Paragon Always Rebels, in which the character has such influence over other good guys that they fall with him or her. See also Fallen Angel, Tragic Villain, and Tragic Monster. Compare FaceHeel Turn, The Dark Side Will Make You Forget. Christopher Booker's sixth basic plot, Tragedy, uses this character arc, with the Fallen Hero as the main character. Almost always gets a Start of Darkness, and often implies Became Their Own Antithesis. Usually revealed in a "Not So Different" Remark moment. Many of these made the protagonist's journey to villainy. The Gunslinger, once wanting to bring justice to the frontier, now wants nothing but vengeance and blood. The Messianic Archetype who wanted to save the world now wants its damnation. Where once the Barrier Maiden wanted to heal the world, she'll now spread misery to speed its destruction. Often, they'll twist healing powers to evil ends, or allow pain to fester by simply denying the use of their powers for good. They'll use their not-inconsiderable powers and abilities to do it, too. Most likely, however, they will help the new heroes in the hopes that they won't suffer the same fate. If the current generation of heroes meets them, the fallen hero will mock how their deeds are useless. They might withdraw from society, become a hermit or drunkard, and ignore the ongoing state of the world.Or they'll be a fusion of the second and third examples and decide that killing/destroying everything is the ONLY way to save EVERYONE from the pain/pointlessness of existence, often becoming a Straw Nihilist and an Omnicidal Maniac.Especially those who only became a hero for fame and glory, rather than for any good cause. Alternately, if they just jump off the slippery slope and embrace chaos and the destruction of humanity as the only solution to their pain, they'll become a straight up cackling Card-Carrying Villain.If the loss of faith with humanity and/or society and government makes them decide to do something drastic to "fix" it, they become an Anti-Villain, most commonly a Knight Templar or Dark Messiah.If they retreat into themselves and fight evil mercilessly to dull the pain, they become an Anti-Hero, though if this fight is motivated by vengeance, they may run the risk of becoming like the very monsters they have sworn to destroy.What they choose to do about it determines what they become: Some Evil Old Folks happened to be this type in their younger days. It might even be a drawn out process of seduction to The Dark Side or fall from grace.
They may even have been an Ideal Hero or another equally optimistic archetype, up until the moment when they suffered something bad enough for them to lose all faith in good and idealism, be it the loss of a loved one, too many good deeds coming back to bite them hard, betrayal by someone they trusted the most, too much distrust from those who should have been allies, or some other faith-shattering event. As the name implies, the Fallen Hero used to be a hero before doing a FaceHeel Turn. Some are made, and none are more tragic than the Fallen Hero.