->''I met [[VillainProtagonist her]] on her first night in costume. She seemed genuinely interested in becoming a hero. I suspected she would go that route on her own, so I didnít push her towards the Wards. I ran into her two more times after that, and the reports from other events match up. She went further and further with each incident. More violent, more ruthless. Every time I saw it or heard about it, I expected her to get scared off, to change directions, she did the opposite. She only plunged in deeper.''
-->--'''Armsmaster''' on Skitter, ''Literature/{{Worm}}''

A recurring scenario where a character, after committing a small act of evil, finds himself becoming more and more evil, very often far more than he originally planned or intended.

Sometimes you can see what you want just beyond your reach--you don't have to jump off the slope, and it's not all that steep anyway, just a few steps on TheDarkSide and you'll have it. Yet what was just a short walk in one direction is not so easily traveled in reverse. Even if you turn back immediately afterwards, you find yourself slipping down the slope faster than you can climb your way up! Eventually you may tire of fighting it and just let yourself continue to slide unhindered, or even worse: choosing to [[ThenLetMeBeEvil embrace the inevitable]] and turn your steps in the direction of your momentum.

This can be done for different purposes:

* A [[{{Aesop}} warning]] that doing some evil, no matter how good an idea it seems, is always a bad idea.
* A [[{{Aesop}} warning]] that once you commit an evil act, no matter how small, you are tempted or otherwise persuaded to commit more and more evil.

For obvious reasons, almost mandatory in StartOfDarkness stories. See MoralEventHorizon for when someone commits an act so heinous and unforgivable that he is now unquestionably evil, and often marks the end point of this character arc. See also HadToComeToPrisonToBeACrook, which is when one of the reasons for falling is spending time in jail, and ThisIsYourBrainOnEvil, for when performing evil act is akin to drug intoxication, and thus very likely to provoke this trope. Do not confuse with JumpingOffTheSlipperySlope, which is when someone on the same side of the heroes but on a morally gray path commits an evil act to prove the rightness of the heroes' path.

Supertrope of HeWhoFightsMonsters, wherein fighting against evil is the thing that causes the person to slip into evil. See also ProtagonistJourneyToVillain

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!! Examples:

[[foldercontrol]]

[[folder: Anime And Manga ]]

* Lelouch and Suzaku in ''Anime/CodeGeass'' become more and more radical during the show's progress, although their goals were noble [[spoiler:and successful.]]
* ''Manga/{{Naruto}}'':
** Sasuke didn't just slide down the slippery slope, he grabbed the sled [[spoiler:Itachi stupidly gave him]] on the way to the edge so he could get down faster. First, he betrayed the village by joining Orochimaru just so he could get strong enough to kill Itachi. He at least had some qualms about killing at this point. [[spoiler:Later on, after killing Itachi, he learns that Itachi massacred their clan under orders from ''four'' of the higher ups (one of which was against it but overruled) in order to stop a civil war that could develop into a ''world war''. Naturally, Sasuke decides that the ''entire village'' has to die because of this. By the time he reaches Konoha, he is not above cold-blooded murder of even his allies just to accomplish his goals.]]
** And he gets worse! Regardless of his statements of genocide, at first he tried to protect the friends that helped him on his revenge quest. Later, however, he'd gotten to the point that anyone who inconveniences him or his goal must die. [[spoiler: Poor Karin.]]
*** [[spoiler:This is later revealed to be caused by a genetic disorder, which drives members of the Uchiha clan insane.]]
* Light from ''Manga/DeathNote'' goes from dark AntiHero to full VillainProtagonist during the course of the series (going from killing criminals to suggest killing lazy people). It's implied that the eponymous ArtifactOfDoom is the [[TheDarkSide cause of this]], not through any supernatural means, but just because [[DrunkWithPower power corrupts]].
* In ''SaintBeast'', Zeus' slip starts with overthrowing the old gods, which he feels [[IDidWhatIHadToDo a measure of regret about]], but thanks (in part) to [[DragonWithAnAgenda Lucifer's]] support, by the time Judas suggests purging the evil angels in heaven, Zeus has basically [[SanitySlippage lost it]] and keeps getting worse.

[[/folder]]

[[folder: Comics ]]

* Winnowilll in ''ElfQuest'' is initially at least reluctant to kill to further her ends. Ironically, her descent into cold-blooded murderess seems to be at least partially due to a botched mind-healing attempt by Leetah.

[[/folder]]

[[folder: Fan Fiction ]]

* Harry in ''[[FanFic/TheDarknessSeries Harry Potter and the Descent Into Darkness]]'' after he hits the DespairEventHorizon when his "friends" abandon him during the Tri-Wizard tournament and, in order to ensure his survival, he begins studying [[BlackMagic the dark arts]].
* In [[http://tvtropes.org/pmwiki/pmwiki.php/FanFic/TheMasksWeWear The Masks We Wear]] Zuko has no qualms firing off lightning against Appa during the invasion of the Fire Nation.

[[/folder]]

[[folder: Film ]]

* Michael Corleone in ''Film/TheGodfather''.
* Creator/ChristopherEccleston's character in ''Film/ShallowGrave''.
* Anakin started to feel doubt and hatred in ''StarWars AttackOfTheClones'', killing an entire population resposible for killing his mother (regardless of individual involvement). If not that, then Sidious manipulating him into killing Dooku probably marks the pivot, [[spoiler:and the children's slaughter the end of the slope]].
* Peter Parker in ''Film/{{Spider-Man}} 3'' slides very slowly. First, he combs his hair differently, then he refuses to pay his rent to his landlord until his door is fixed, and after that he finally performs evil acts, such as emotionally manipulating his friends and co-workers, punching his love interest (accidentally), [[ArsonMurderAndJaywalking and performing a very awkward jazz number for no obvious reason.]]
* Stephen in ''Film/TheIdesOfMarch'' goes from idealism to cynicism and worse.
* Magneto in ''Film/XMenFirstClass''; a really good and interesting example in that he starts the movie already as an AntiHero and spends most of the movie establishing his attitude that would cause him to slip into evil before he actually does so. And while he's undeniably a JerkAss in opposition to the heroes by the end of the movie, he still isn't evil and never really crosses the MoralEventHorizon.
* Discussed in ''Film/TheEliteSquad'' with regards to {{Dirty Cop}}s.
--> The first time is always a good cause. But once you steal for the force you'll also steal for your family. That's how the system works.
* Dr. Norton in ''Film/RoboCop2014''. At the start he doesn't want anything to do with weaponising his cyborg technology, but Sellars talks him into working on [=RoboCop=]. As the film goes on he starts making bigger compromises, such as tinkering with Alex's brain and body chemistry, which have the effect of reducing his humanity. [[spoiler:Eventually however, [[HeelRealization he realizes just how far he's gone]] and seeks to repair the damage.]]
** Sellars himself, sorta. He begins the film as a guy who simply wants to sell his machines to the American government, and unlike his counterpart in the original, those machines actually work. He slowly toys more and more with Murphy, treating him less than a man and more of a useful product as the plot goes on, and once he utters [[spoiler:"you know what's better than a hero? A dead hero"]], you know there is no turning back.

[[/folder]]

[[folder: Literature ]]

* In ''Literature/MemorySorrowAndThorn'', this trope in a nutshell is the Backstory of the Big Bad, the Sitha prince Ineluki. Once a purely heroic figure, his ambition and willpower darkened when the Sithi's lands were invaded by savage humans. Dismayed by his people's despair in the face of their approaching doom, he delved into Things Man Was Not Meant To Know and constructed a weapon so terrible that his father, the king, insisted he destroy it. Maddened by this rejection and by his torments, Ineluki murdered his father and took the crown, leading a final, futile resistance against the humans that ended in his death via DangerousForbiddenTechnique. He is at the start of the story the BigBad and an OmnicidalManiac.
* Conall Haldane in the ''{{Deryni}}'' novels ''The King's Justice'' and ''The Quest for Saint Camber'' goes from merely being a RoyalBrat and SoreLoser to committing murder and treason. He says as much at his trial: "I didn't start out to betray you, Kelson," he sobbed, "but things -- happened. It wasn't fair!"
* This is the big reason why the Laws of Magic exist, and why the Wardens exist to enforce them in ''TheDresdenFiles.'' The [[BlackMagic types of magic prohibited by the Laws]] all lead the caster to want to use them more often, eventually turning him into a villain. The Wardens will sometimes grant clemency on the first offense if it can be proven that the offender didn't know any better ''and'' a senior wizard offers an apprenticeship to oversee the offender's redemption. In any other case, summary execution is prescribed.
** Also, this is a major fear of Harry's after [[spoiler:taking up the mantle of the Winter Knight, more so after he finds out that this basically dooms him to becoming a monster.]]
** [[TabletopGame/TheDresdenFiles The roleplaying game]] reflects this by giving Lawbreakers mandatory stunts that cost them refresh whether they like it or not but [[ItGetsEasier provide them with bonuses towards breaking the same laws again]]. Of course, they technically never ''have'' to use those bonuses (which come with additional drawbacks if one keeps taking advantage of them anyway, literally changing who the character is over time as he or she gets twisted by the ongoing practice of forbidden magic), but once things get desperate and the temptation great enough...?
* A major fear for the kids in ''Literature/{{Animorphs}}''.
--> RACHEL: (narrating) "I know it's wrong," he said. "But it doesn't matter. We have to do it. It's a war. We have to win." I had to laugh. People sometimes think that I'm a bad person, a violent person. But even I know that the words "we have to win" are the first four steps down the road to hell.
* In SherlockHolmes story "A man with a twisted lip", the resolution is that a respectable journalist first poses as a beggar for the sake of research, then discovers this pays way more than his job (if done artistically enough), then uses begging to get out of a medical debt, and finally abandons journalism altogether, becoming professional beggar.
* In ''Gingema's Daughter'', first book in Sergey Sukhinov's ''Emerald City'' series, is about the adventures of Corina, originally an ordinaly, if somewhat lazy, girl. She starts her way as undertudy of Gingema, then runs away to travel with her wolf companion. She lives by different families, usually helping them magically in secret. But gradually, she decides that BeingGoodSucks, since everybody bothers you with requests, and being feared is as important as being loved. She deceives the Woodsman to do her bidding by pretending to be the daughter of his former sweetheart, and ultimately manipulates him into deposing the Scarecrow, thus becoming the ruler of Emerald city. The rulership she establishes is a CrapSaccharineWorld: there is food for free and low taxes, but do cross Corina in any way and you are dead or turned into a small animal. By the second book, she kills Ellie's parents and becomes a fully-fledged villain.
* Made explicit in CS Lewis's ''Literature/TheScrewtapeLetters'', which is a satirical exploration of Christian theology, detailing a senior demon's advice to his nephew on securing the damnation of a human - ''the safest road to hell is the gradual one - the gentle slope, soft underfoot, without sudden turnings, without milestones, without signposts''.

[[/folder]]

[[folder: Live-Action TV ]]

* ''TwentyFour'': This is one of of the main points behind Jack's arc in the final season: after losing another loved one thanks to the conspiracy of the season and being denied justice against her killers when the President of the United States betrays him, he '''snaps''' and goes on a RoaringRampageOfRevenge to slaughter everyone behind said conspiracy. The thing that kicks him down the path is when he executes one of those involved in the plot that didn't even have to do with the murder. After this, his actions get much more brutal and violent with each episode, with him even starting to unintentionally endanger innocent people as he slowly becomes just as bad as the villains. [[spoiler:Chloe manages to snap him back to his senses in the series finale before he crosses the last line and unwittingly starts World War III.]]
* ''BoardwalkEmpire'': Jimmy Darmody has a conversation with his wife in the second season about how every time he draws a line in the sand, he winds up having to cross it to be a successful gangster. This eventually results in him doing all sorts of things he never thought he'd do, and that other people are horrified by, including [[spoiler:ordering the assassination of his father figure Nucky]].
* ''Series/BreakingBad'': The whole point. Walter White starts as a chemistry teacher who gets cancer, so he begins to make meth as a way to leave money for his family. Then, his actions become not only much less justified, but also he goes on to kill and begins some big schemes.
* ''Series/{{Merlin}}'': Morgana has a long-term one of these over the course of the second and third series. Of course, this is usually conveniently forgotten about when she is not directly the antagonist of each plot of the week.
* ''Series/OnceUponATime'': Regina becomes increasingly dark and angry [[spoiler:after her mother, Cora, kills her boyfriend]]. She has evil thoughts about killing Snow, who she blamed for her telling Cora about Regina, and Daniel. After she banishes her mother by using magic, she tells Rumplestiltskin "I'll never use magic again." He asks why, she says [[EvilFeelsGood "Because I ''loved'' it".]] [[StoicWoobie And she still manages to remain good]], despite [[TheDarkSide this causing an addiction]], and [[HeroicWillpower she refuses to obey Rumplestiltskin]]. Then, he gives her a HopeSpot to make her grow insane and think that she should get revenge because it is all she will believe that she has left to do. It works.
* ''Series/{{Revolution}}'': Ever since Rachel Matheson made a deal with the devil named Randall Flynn to ensure Danny's survival from birth ("[[Recap/RevolutionS1E7TheChildrensCrusade The Children's Crusade]]"), this trope has been happening to her. She killed the Wiry Stranger when he tried to steal food from the Mathesons ("[[Recap/RevolutionS1E2ChainedHeat Chained Heat]]"). She turned herself into Miles's custody to allow her family to escape his clutches ("[[Recap/RevolutionS1E4ThePlagueDogs The Plague Dogs]]"). She apparently refused to reveal or do anything for 7 years...until Danny ends up in Monroe's custody ("[[Recap/RevolutionS1E5SoulTrain Soul Train]]"). Then she reveals enough information to get her old colleague Bradley Jaffe and his daughter in trouble. She ended up killing Jaffe to her own life and Danny's ("[[Recap/RevolutionS1E9Kashmir Kashmir]]"). She insists on destroying the pendants rather than letting Team Matheson use them. She pulls out a nanotech capsule from [[spoiler: Danny's corpse]] ("[[Recap/RevolutionS1E11TheStand The Stand]]"). She slapped Charlie where her daughter tried to call her out on leaving them all those years ago ("[[Recap/RevolutionS1E12Ghosts Ghosts]]"). On Rachel and Aaron's journey to the Tower, Rachel tries stealing the information she needs from her old colleague Jane Warren and nearly got killed for it ("[[Recap/RevolutionS1E14TheNightTheLightsWentOutInGeorgia The Night the Lights Went Out in Georgia]]"). Then she steals food from a tribe, shoots the tribe leader when he threatens to kill them and gets in big trouble for it ("[[Recap/RevolutionS1E16TheLoveBoat The Love Boat]]"). Finally, she leads a family to believe that she can save their boy from death, and then reveals to Aaron that she's not trying to restore power for anyone's good, but rather to give the people the power to kill Monroe as revenge for killing [[spoiler: Danny]]. She is also willing to throw Aaron under the bus to achieve her revenge ("[[Recap/RevolutionS1E17TheLongestDay The Longest Day]]"). She has been sinking to new lows as the series goes on.
* ''{{Smallville}}'': LexLuthor has this happen to him over the course of this show, going from close friend of Clark's and genuinely good guy to evil villain over the course of the series. Lampshaded when he tells Ryan that 'Evil is a journey, not a light switch'.
* ''Series/StarTrekDeepSpaceNine'': Gul Dukat was always a nasty authoritarian, but in early seasons would help the good guys on a pragmatic basis. After the Dominion War started, he aligned Cardassia with the Founders. When that didn't work, he became a full-on OmnicidalManiac.

[[/folder]]

[[folder: Tabletop Games ]]

* ''TabletopGame/{{Deadlands}}'' uses this as part of the two most extreme [[PayEvilUntoevil Dark Gray Hat]] character types. Vampires, in Deadlands Classic, and Anti-Templars, in the post-apocalyptic Deadlands: Hell on Earth setting. Both have backstories that they will inevitably fall to corruption or die, and in a case of GameplayAndStoryIntegration, these are backed by mechanics that eventually determine when the player becomes invalid.
* In ''TabletopGame/{{Ravenloft}}'', performing an evil deed and certain other actions result in what is called a Dark Powers Check, to see if the forces that govern the Demiplane of Dread take notice. If they do, the Dark Powers simultaneously imbue them with a blessing and smite them with a curse. These powers and curses grow with each subsequent failed check, until inevitably the victim becomes a monster, perhaps even a DarkLord in their own right.
* This is a common feature through the ''TabletopGame/NewWorldOfDarkness'', but it's most applicable to ''TabletopGame/VampireTheRequiem'' and ''TabletopGame/DemonTheDescent''.

[[/folder]]

[[folder: Video Games ]]

* A major theme in ''Franchise/{{Bioshock}}'', where the two Big Bads during the [[FlavorText backstory]] change from rude ruler to the people they hate most (in the [[VideoGame/BioShock first]], an objectivist became first a dictator, then a totalitarian dictator, in the [[VideoGame/BioShock2 second]], an Altruist became more and more selfish and [[spoiler:ends up sacrificing everything to save herself]]). The {{Aesop}} here is the danger of fanaticism.
* In ''VideoGame/MafiaTheCityOfLostHeaven'', Tommy starts off trashing a rival family's cars and finishes the game as a stone-cold killer.
* ''[[VideoGame/KirbySuperStar Kirby Super Star Ultra]]'': [[spoiler:Marx]].
* Arthas in ''VideoGame/WarcraftIII'' is initially a WellIntentionedExtremist when he decides to kill the citizens of Stratholme [[ZombieInfectee who ate infected grain which turns humans into zombies and would soon morph into the undead]]. After unwittingly [[DealWithTheDevil selling his soul to the Lich King]] in order to make use of the sword called Frostmourne, [[TheEvilPrince he kills his father, the king of Lordaeron]], destroys the elven capital of Quel'thalas, and aids in the opening of a demonic portal for the Burning Legion.
* In ''VideoGame/WorldOfWarcraft'', the [[BloodKnight war-mongering]] [[FantasticRacism racist]] Garrosh Hellscream started as a crude and needlessly aggressive leader who simply wanted what was best for the Horde. Over the course of his rule he became increasingly harsh on non-Orc members of the Horde and began to dream of conquest, by whatever means necessary, alienating allies and uniting his enemies. His creation of [[TheHorde the True Horde]] and use of an Old God's power was the final step in becoming a villain.
** The Forsaken under Sylvanas have become more explicitly villainous after Sylvanas experienced TheNothingAfterDeath. In her drive to prolong her existence as long as possible she has not only gone to extreme lengths to capture contested territories, but has also begun to turn on the Ebon Blade and even create new Forsaken by raising her fallen enemies as new Forsaken. Even ''Garrosh'' thinks she's going too far, but [[FantasticRacism that just may be his personal hatred of the undead]].
* Joshua Graham of VideoGame/FalloutNewVegas began as translator and missionary, but slowly compromised himself until he became known as one of the [[TheDreaded cruelest, most dangerous men in the Mojave]]. [[TheAtoner He gets better, though.]]
* ''VideoGame/SpecOpsTheLine'': [[spoiler:Walker's]] entire character arc is one of these.

[[/folder]]

[[folder: Webcomics ]]

* In Book 9, Part V of ''WebComic/SchlockMercenary,'' General Xinchub is revealed to have gone through one of these:
-->'''Xinchub:''' I sold my soul a long time ago, believing that I was helping Humanity, and all our Terran cousins. I've done all kinds of atrocious things, and somewhere along the line I started to enjoy them.
-->'''Ceeta:''' Happy memories?
-->'''Xinchub:''' Yeah, good times, good times.

[[/folder]]

[[folder: Web Original ]]

* In ''WebVideo/DoctorHorriblesSingAlongBlog'', Dr. Horrible starts off as an [[IneffectualSympatheticVillain ineffectual]] AntiVillain, maybe with [[WellIntentionedExtremist good intentions]], but through constant humiliation, [[LoveMakesYouEvil losing his love interest]] to the {{Jerkass}} SmugSuper Captain Hammer, his own urge to join the Evil League of Evil, and the League's threat that he [[IfYoureSoEvilEatThisKitten prove himself by killing someone]] or be killed by the League for wasting their time, he takes a long ride down the evil slope, culminating in the attempted murder of Captain Hammer.
* The trope comes up a few times in ''Literature/{{Worm}}'':
** [[http://parahumans.wordpress.com/2012/05/17/interlude-10-5-bonus/ Armsmaster's description of Skitter's career fits the template.]]'
*** Armsmaster's description, however, neglects to mention the detail that [[spoiler: He was using her to spy on the Undersiders for his own gain.]] The truth is that she wasn't evil until he pushed her away.
** One of the people Skitter recruited in the wake of [[spoiler:Leviathan decimating the town]], Sierra Kiley, mentions in her narration during [[ADayInTheLimelight Interlude]] [[http://parahumans.wordpress.com/2012/10/11/interlude-14/ 14]] that she worried that Skitter would try to lead her down this path, and was [[AvertedTrope surprised it hadn't happened.]]

[[/folder]]

[[folder: Western Animation ]]

* SethMacFarlane likes this trope, although he [[PlayedForLaughs plays it for laughs]]. He's {{Flanderized}} two of his star characters, Peter Griffin of ''WesternAnimation/FamilyGuy'' and Roger Smith of ''WesternAnimation/AmericanDad'', into FauxAffablyEvil {{Jerkass}}es. Roger's DisproportionateRetribution to Steve for taking his cookie was arguably the start of his crueler aspects taking over his role, while Peter's probably began with the lighter abuse of Meg in early post cancellation episodes.

[[/folder]]

[[folder: Truth In Television ]]

* The subject of [[http://www.nova.edu/ssss/QR/QR9-2/oleson.pdf this journal article]] made friends with a drug dealer, then started to help him run his gang, then shot a man in self-defense... By the end of his criminal career, he had killed fifteen people and was prepared to commit murder merely to "safeguard his reputation."

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