A recurring scenario where a character, after committing a small act of evil, finds himself becoming more and more evil, committing more and worse acts, 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 The Dark Side 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 may find yourself slipping down the slope faster than you can climb your way back up! Eventually you may tire of fighting it and just let yourself continue to slide unhindered, or even worse: choosing to embrace the inevitable and turn your steps in the direction of your momentum. Oftentimes, all the evil you do after that first fatal act makes you lose sight of who you were before everything.
This can be done for different purposes:
- A warning that doing some evil, no matter how good an idea it seems, is always a bad idea.
- A warning that once you commit an evil act, no matter how small, you are easier to be tempted or otherwise persuaded to commit more and more evil.
For obvious reasons, almost mandatory in Start of Darkness stories. See Moral Event Horizon for when someone commits an act so heinous and unforgivable that he is now unquestionably evil, and often marks the endpoint of this character arc. See also Had to Come to Prison to Be a Crook, which is when one of the reasons for falling is spending time in jail, and This Is Your Brain on Evil, for when performing an evil act is akin to drug intoxication, and thus very likely to provoke this trope. A common way of subverting this is for the character to make a Sudden Principled Stand when it becomes clear that the character has found a foothold on the seemingly slippery slope and will sink no further. Do not confuse with Jumping Off the Slippery Slope, 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.
A Super-Trope to He Who Fights Monsters, wherein fighting against evil is the thing that causes the character to slip into evil. See also Protagonist Journey to Villain and It Gets Easier. Can coincide with Big Bad Slippage.
- Lelouch and Suzaku in Code Geass become more and more radical during the show's progress, although their goals were noble and successful.
- Dragon Ball Super features Zamasu, a Supreme Kai in training of Universe 10. He starts out as distrustful of mortal beings, claiming they are barbaric and cannot improve. He is immediately shown as having ties, albeit distant, to Goku Black, and as time goes on his resent for mortals only increases, reaching what seemed to be its peak when Zamasu and Gowasu travel to a planet of primitive aliens who barely improved with time. Zamasu mercilessly kills one of the aliens when it attacks, and reacts almost euphorically. This begins a slippery slope for him, and he begins contemplating exterminating all mortals. With the arrival of Goku, investigating Goku Black and his obsessive desire to fight, Zamasu becomes even more disgusted with mortals (and Goku specifically) upon realizing Goku has achieved godly power and defeated him. Eventually it's revealed he is the one behind the devastation of Future Trunks' timeline, as in the future of the main timeline, he finally snaps and kills his master Gowasu, uses the Super Dragon Balls to switch bodies with Goku and travels to Trunks' timeline to begin his plan of wiping out all life in the universe. As he gets stronger he becomes even more unstable and sets his sights on the entire multiverse.
- In Death Note, protagonist Light Yagami's initial instinct upon acquiring the titular notebook was to eliminate all crime on Earth to create a peaceful Utopia. Towards the end of the very next episode, however, Light ends up killing a man during (what he believed to be) an international broadcast for calling him evil. While it turns out said man was a criminal on death row, Light didn't know that at the time. Things only get worse from that point forward.
- By the mid-point of Fire Punch, Agni's mental state become the biggest problem for himself and everyone else. Agni's enemies and survivors of the crossfire name him "Fire Punch", and sometimes he considers living up to his fearsome reputation.
- Riddhe Marcenas of Mobile Suit Gundam Unicorn starts as an honorable young officer who has some issues with his family, who saves Banagher and his (surviving) classmates and decides to help Audrey after identity as Mineva Lao Zabi is revealed. When he finds out just how badly his family is involved in wrecking the Universal Century, however, Riddhe plunges into fatalism. After clashing with the idealistic and increasingly pacifistic Banagher, becoming fatalistic and deciding that it's better to preserve a corrupt but stable status quo than to try to improve the world, and being rejected by Mineva, Riddhe is in a pretty bad mood when Marida trashes his mobile suit. He proceeds to dive headlong into his own personal zealotry, which mainly involves wiping Gundams and Newtypes out.
- Sasuke didn't just slide down the slippery slope, he grabbed the sled 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, refusing to kill Naruto in order to unlock the Mangekyo Sharingan, and even during his training he left his opponents alive, simply stating that the only one he wants to kill is Itachi. Later on, after Itachi dies at the end of their battle, 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 the Kage Summit, 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 be abandoned or killed. Poor Karin. He then later tries to kill Naruto after deciding to become a Shadow Dictator so that the world will fight him instead of each other, but is beaten by Naruto and made to see sense finally.
- This is later revealed to be caused by a genetic disorder, which drives members of the Uchiha clan insane as that which they love ends up being destroyed in front of them and causing them to lash out at the world in increasingly self-destructive ways.
- A major theme of Overlord (2012) is that Ainz Ooal Gown, despite starting out as an Anti-Hero or Anti-Villain, is slowly becoming just as much of a ruthless, bloodthirsty tyrant as his underlings and the rest of the world see him as. Interestingly though, in the setting he is in he still can be seen as a good guy.
- In Saint Beast, Zeus' slip starts with overthrowing the old gods, which he feels a measure of regret about, but thanks (in part) to Lucifer's support, by the time Judas suggests purging the evil angels in heaven, Zeus has basically lost it and keeps getting worse.
- Officer Bill Petit in Batman: No Man's Land is a textbook case of a Well-Intentioned Extremist going Drunk with Power:
- He starts off as a loyal member of Commissioner Gordon's "Blue Boys" trying to maintain order in Gotham, and though he advocates a more ruthless approach to the various psychopaths and criminals they have to deal with, it's hard to argue against him in light of the fact that there's no longer even a Cardboard Prison to keep them in, and innocent people are being murdered every day as the gangs fight for turf.
- Later, while still a member of Gordon's team, he publicly executes one known murderer to convince the other criminals that the Blue Boys aren't kidding when they tell them not to cause trouble. Gordon calls him out for this, but Petit's reasoning is sufficiently sound that they can't really call him a murderer, and they let him stay a member of their team.
- Later, he leaves Gordon's team out of disgust for their maintaining their soft approach to crime even when it's clearly not working, but is justified enough that a large number of the Blue Boys leave with him, and neither Gordon nor Petit consider each other enemies at this point.
- Then, after realizing Oracle is an invaluable source of information, he launches an attack on her tower to bring her in alive, but tries to kill Nightwing when he intervenes, prompting Huntress (who had been swayed by his arguments and actually joined him willingly) to intervene, but Petit and Huntress agree to keep working together.
- By the end of his arc, after Batman's return and aid to Gordon has made the Blue Boys more effective, he's become so paranoid about losing face in front of his own men and criminals (he calls it "loss of morale") that he forces all the residents of his territory to attend his "Christmas feast", and won't let them leave without his permission, even when the Joker attacks. Finally, he starts shooting left and right at people he thinks are the Joker, even though his own people are warning him that it's a Disguised Hostage Gambit, and then when one of his most loyal subordinates tries to leave to get reinforcements, Petit shoots him on the spot while screaming "No one leaves without my permission!"
- Winnowill 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.
- This was what led to Superman's fall to evil in Injustice: Gods Among Us. Following the loss of Lois Lane and their unborn child and his murder of the Joker in revenge, Superman became more and more brutal and ruthless in combatting ever greater threats to his planet until he became the evil ruler of the Regime from the game.
- Though he's yet to become completely evil, a major theme of The Walking Dead is how Rick becomes more and more amoral as time goes on and he becomes more desperate. As one reviewer put it, it's like seeing what it would take to make Andy Griffith have a mental breakdown and eat the citizens of Mayberry.
- Between Dreams and Memories Universe:
- Dream was once a benevolent, good-natured man who founded the DreamSMP so he could provide a home for runaways and outcasts. However, by the time of the story, he's become a Drunk with Power tyrant who's firmly a Fallen Hero. Hints of his previous good nature slip out multiple times over the course of the story, but he tends to ruin them with his own displays of pettiness and sadism and he only continues to slide firmly into villainy over the course of the fic. By the time of the sequel, he's become an irredeemably cruel, toxic monster and has lost all of his redeeming qualities.
- Wilbur starts off as a genuinely well-meaning man, who is hampered by his own selfishness, short temper, and paranoia which makes him pretty unpleasant to be around. As he goes through a Trauma Conga Line after Schlatt exiles him that culminates in him realizing that he's a Source, an already unstable Wilbur snaps and decides to embrace what he sees as his true nature.
- Code Prime: Suzaku has been undergoing this due to working side by side with Megatron, culminating in Chapter 18 of R1, where he becomes the first human member of the Decepticons. Thankfully, he's pulled out of this at the end of R1 and joins the Autobots and Black Knights.
- In Death Note fanfic Fade, L gets his hands on a Death Note, containing a part of the story of Kira's rise to power. Trying to stop that from happening leads to L's own Start of Darkness as he becomes more and more similarand arguably worsethan the killer he's trying to find.
- Harry in Harry Potter and the Descent Into Darkness after he hits the Despair Event Horizon when his "friends" abandon him during the Tri-Wizard tournament and, in order to ensure his survival, he begins studying the dark arts.
- In The Masks We Wear, Zuko has no qualms firing off lightning against Appa during the invasion of the Fire Nation.
- Mastermind: Rise of Anarchy:
- The more Bakugou ventures out as the vigilante 'King', the further he slides towards villainy, taking out his frustrations by beating up any 'low-life crooks' unfortunate enough to cross his path. His refusal to acknowledge his mistakes and anger upon hearing others describe exactly what he's doing doesn't help one bit, leading up to his accidentally murdering Ogawa in a fit of rage.
- Principal Nedzu decides to set up Uraraka Ochako to become the next Symbol of Peace, transforming into The Svengali in the process as he encourages their Survivor Guilt and pushes them further and further past their limits and into the public eye.
- Murderer's Row: Church started off as a Justified Criminal who regularly commits robbery to support himself and his younger brother. However, after the two are forced to go on the run after Church kills their abusive father in self-defense, Church winds up being press-ganged into joining a crime syndicate and becomes increasingly amoral and murderous until he ends up as an unrepentant and ruthless crime boss, albeit one with a few scruples.
- Depicted through flashbacks in Steal Your Way In. What starts with Yoshi committing tax fraud to help his people catch up with the rest of the world gradually turns into worse crimes with increasingly flimsy justifications until he's a remorseless criminal kingpin.
- In XCOM: From the Ashes of Temples, Commander Bradford gets hit hard by The Chains of Commanding and starts making more and more ruthless decisions in his desperation to keep XCOM running. Even Vahlen calls him out on it.
- Dungeons & Dragons: The Book of Vile Darkness puts a weird twist in it. The protagonist Grayson is essentially The Paladin, only he belongs to an order that's no longer recognised by their god. He swears an oath to uphold certain virtues, but, anticlimactically, he doesn't receive the blessing he's supposed to get from Pelor — just as nobody else has for a while. Then he finds himself having to pretend to team up with the villains to save his father, and this trope seems to apply in that he breaks one part of his vow after another. And only after all that he becomes a real hero, having never lost sight of his goal, and is blessed by Pelor. It makes for nice irony if nothing else.
- Discussed in The Elite Squad with regards to Dirty Cops.
The first time is always for a good cause. But once you steal for the force you'll also steal for your family. That's how the system works.
- The Godfather:
- Michael Corleone in the first movie. He's trying to put some distance between himself and his mobster family at the beginning of the film, although he doesn't disown it. When a gang war puts the family members in peril, he slowly starts helping, first by preventing a hit on his ailing father at a hospital, then by rationalizing a vendetta against a policeman as a necessary strictly business move. As he escapes, he tries again to get away from it all, only to be dragged back by the assassination of his first wife. From then on, he starts becoming more and more ruthless.
- Vito Corleone in The Godfather II. The flashbacks show him start as an innocent boy in the middle of a feud between his family and a local Sicilian mobster. When his parents and brother are killed, he's whisked away to America by relatives. He grows up to be an ordinary grocer until he loses his job because of a New York gangster. When he helps a smuggler hide a gun, the by-now married Vito becomes a small-time criminal himself out of necessity to feed his growing family. By the end of the film, he's the Affably Evil overlord of a well-established criminal empire.
- Happens to Danny with greed. He first seems motivated by trying to at least keep Uncle Joe safe from the other relatives (who are quite happy to have the man declared incompetent and put into a home), only for him to eventually become as manipulative and as greedy as everyone else, culminating in him hiring an actor to portray his estranged father just so that he could side with Joe in a scripted argument. When confronted with his real father, he finally realizes what he has done and he more or less describes the trope: one thing didn't seem wrong, then another thing didn't seem wrong until finally nothing seemed wrong.
- Ed himself sums it up quite nicely:
Ed: Every time you draw a line in the dirt, you say, "Okay, I go just this far and no farther." He draws another line, just an inch farther and you say, "Why not? It's just another inch, I've already come this far already," and one day you look back and you can't even see where you started. Why don't we all agree to stop here? Let this bimbo have his money. I mean, isn't our self-respect worth more than any inheritance?
- Judgment at Nuremberg: Janning describes himself and other Germans who had gone along with the Nazis as essentially this, doing increasing worse things in the name of patriotism until they had unleashed the Holocaust. It's mentioned he helped found the Weimar Republic, eventually ending up helping the Nazis, whose regime destroyed not only the Republic but everything it stood for.
- RoboCop (2014):
- Dr. Norton. 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. Eventually, however, he realizes just how far he's gone and seeks to repair the damage.
- Sellars himself. He begins the film as a guy who simply wants to sell his machines to the American government, and unlike his counterpart Dick Jones in the original, those machines actually work. He slowly toys more and more with Murphy, treating him less as a man and more of a useful product as the plot goes on, and once he utters "you know what's better than a hero? A dead hero", you know there is no turning back.
- Saw: Jigsaw did target people who did him wrong or he believed were wasting their lives, but his reasons (speaking of himself and not his apprentices who sought to sabotage his philosophy) became pettier over time.
- In general, his first victims were previously patients in Jill's drug recovery clinic, which fitted with the point of his tests being a form of rehabilitation. By contrast, his later victims either pretended to be him or have some connection to him, denied him health insurance, or were callous when they told him he had inoperable cancer.
- The earliest sign of this was in the first movie, when he forced Amanda to fish out the key to the Reverse Bear Trap from Donnie Greco's stomach, not telling her that he was still alive and she killed him in a frantic attempt to get the key.
- Further onward, he chose a janitor in Saw VI for smoking so he could punish William Easton for denying him insurance, and he chose various victims throughout the series for simply lying; the only justified case was Bobby Dagen in Saw 3D, since his lies were about surviving Jigsaw just to gain money and fame. Even still, he brutally sacrifices Bobby's wife by burning her alive just to further punish him (even though she did nothing to deserve it).
- Peter Parker in Spider-Man 3 slides very slowly as the Symbiote starts to influence him. 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), and performing a very awkward jazz number for no obvious reason. Thankfully, he snaps out of this before things go too far and gets rid of the Symbiote, only for the thing to switch hosts to Eddie Brock, who becomes Venom.
- Star Wars: Anakin started to feel doubt and hatred in Attack of the Clones, killing an entire population of Sand People in revenge for his mother's death (regardless of individual involvement). If not that, then Sidious manipulating him into killing Dooku in Revenge of the Sith probably marks the pivot, and the slaughter of the children of the Jedi Temple the end of the slope.
- Loki in Thor. First, he lets three Frost Giants into Asgard for "a bit of fun", which results in the death of a couple of guards. Then he manipulates his brother into going to Jotunnheim and simultaneously warns the guards to ruin Thor's reputation, which backfires into Thor's banishment. Later he makes Thor believe that Thor is guilty of Odin's death to keep him dispirited and stranded on Earth. When Thor discovers it's a lie, Loki sends the Destroyer to murder his brother. And finally, he attempts to commit genocide by using Bifrost to destroy Jotunnheim with all its inhabitants.
- X-Men Film Series:
- Magneto in X-Men: First Class; a really good and interesting example in that he starts the movie already as an Anti-Hero 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 Moral Event Horizon.
- Within 11 years between X-Men: First Class and X-Men: Days of Future Past, he became involved with the JFK assassination (while he claims to have been attempting to stop it) and launched an attack against the White House.
- A major fear for the kids in 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.
- Conall Haldane in the Deryni novels The King's Justice and The Quest for Saint Camber goes from merely being a Royal Brat and Sore Loser 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!"
- The Dresden Files:
- This is the big reason why the Laws of Magic exist, and why the Wardens exist to enforce them. The 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 taking up the mantle of the Winter Knight, more so after he finds out that this basically dooms him to becoming a monster.
- The roleplaying game reflects this by giving Lawbreakers mandatory stunts that cost them refresh whether they like it or not but 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...?
- Gingema's Daughter, the first book in Sergey Sukhinov's Emerald City series, is about the adventures of Corina, originally an ordinary, if somewhat lazy, girl. She starts her way as understudy 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 Being Good Sucks, 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 Crapsaccharine World: 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.
- In the Father Brown stories, Father Brown persuades the Gentleman Thief Flambeau to reform and become a private detective by convincing him that he's deceiving himself about the possibility of remaining a professional criminal without doing anything genuinely evil (in this case, leaving an irritating but innocent man as the Fall Guy). Flambeau listens, gives up his criminal ways (well, acrobatics and lockpicking are always useful) and becomes a private detective.
- A Discussed Trope in Hard Rain (aka A Lonely Resurrection) by Barry Eisler, with various characters being deliberately exposed to killing (Fight Clubbing being used to recruit assassins), prostitution (a stripper in a nightclub who's being offered money to sleep with clients) and espionage (a CIA informer is asked to sign for money he's being given. The first few times he might refuse or put an ineligible scrawl, but eventually he'll get careless and put his proper signature which can be used for blackmail) to desensitize them to those worlds so they can be drawn into them.
- In The Iron Teeth web serial, Blacknail the goblin starts out small and weak. At first he sticks to petty crimes such as theft, but in order to gain power in his "tribe" of outlaws he begins to kill.
- A major theme of The Lost Fleet. The Syndicate Worlds were a brutally repressive and unpleasant oligarchy to start with, but in a full century of bloody and seemingly unwinnable war, The Alliance has started started resorting to tactics as ruthless and immoral as their enemies. It takes recently-defrosted Human Popsicle Captain John Geary bringing an outside perspective -not to mention really blowing his stack in public, something he does no more than five times in seven volumes- to shock some of the other Space Navy officers into realising just how far they've fallen.
- In Memory, Sorrow and Thorn, 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 Dangerous Forbidden Technique. He is at the start of the story the Big Bad and an Omnicidal Maniac.
- Made explicit in CS Lewis' The Screwtape Letters, 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.
- In the Sherlock Holmes story "The Man with the 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 a professional beggar.
- Star Wars Legends: In Kenobi, Orrin Gault is eventually revealed to be this. He started by embezzling money from the Settlers' Call Fund in order to make payments on his debts. When attacks by Tusken Raiders became rarer courtesy of Anakin Skywalker, more and more settlers canceled their subscriptions, so Orrin and his family began staging raids to make them return. They never give the settlers more than light injuries, but are not above killing actual Sand People in "retaliation". At the climax, he attempts to murder Ben after the latter witnessed them faking a raid and finds out he's a Jedi in the process; even so, Ben lets Orrin go, only for the latter to refuse to turn around and plan to sell Ben's identity to the Galactic Empire. His kids don't fall far from the tree and decide to kill Annileen Calwell, who had been the family's best friend until the day before.
- Lampshaded by Jenny Bunn in Kingsley Amis' Take a Girl Like You:
This business of why shouldnt we do this, and we do it, and so then why shouldnt we do this, and we do that, because its only a tiny bit more than the one before, and it would be so nice its leading on and its not leading on, its like with a bag of sweets, just one more and well put them away, except one mores only just the one more, isnt it? And they are nice, so theres never anything against Oh, all I mean is people forget things and lose their heads. You know how they do.
- The trope comes up a few times in Worm:
- Armsmaster's description of Skitter's career fits the template.
- One of the people Skitter recruited in the wake of Leviathan decimating the town, Sierra Kiley, mentions in her narration during Interlude 14 that she worried that Skitter would try to lead her down this path, and was surprised it hadn't happened.
- 24: 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 Roaring Rampage of Revenge 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. 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.
- Boardwalk Empire: 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 ordering the assassination of his father figure Nucky.
- Breaking Bad: 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.
- Very common in Buffy the Vampire Slayer and Angel, with examples including Faith, Warren and Amy. The heroes are also commonly battling with this themselves - Willow eventually turned evil for a brief but memorable period, and Wesley also got fairly dark.
- This got fully-developed with Faith - after accidentally killing a human on pure instinct before realizing he was not a vampire, she tries to wash her hands of it (both metaphorically and literally) and convince herself (and others) that she truly doesn't care; then she tries to deflect blame on Buffy... Angel does a Lampshade Hanging on this trope when he says that now that Faith has killed, "she's got a taste for it now"; when Wesley botches his attempt to talk her around she teams up with the Mayor, she falls deeper until she ends up in a coma. Eventually though, unlike Warren and Amy above, she becomes The Atoner.
- Doctor Who: It's been heavily implied that the Doctor is terrified of this happening to him. And in fact, during his first adventure, he almost killed a caveman with a rock, until Ian intervened. Which is why he likes to have humans around him at all times: because they keep his bad side in check. Donna Noble's actions in "The Fires of Pompeii" are a good example.
- Hemlock Grove: Roman slowly becomes more immoral as time goes on. Early episodes where he shows his depravity such as him raping a girl from his school are initially offset by his horrible domestic situation and his perpetual self-loathing. By the end of the series he's become so unhinged that he's simply murdering people left and right, forcing Peter to finally turn against him.
- Kamen Rider Gaim: Kureshima Mitsuzane. He starts off as an overall nice guy, sidekick, and good friend to the Hero, and the brains to his brawn. As the series progresses, he starts showing a darker side to himself. He begins attempting to manipulate his friends and outright lying to them, hiding vital information, and allying with the Yggdrasil Corporation they are against. While all this was done in order to protect his friends, he starts feeling that using those methods is the only way to accomplish that and keeps doing so. Once Kouta, the series protagonist, starts unknowingly hindering his plans to keep everyone he cares about safe, he slowly starts to lose it and the situation gets even worse when his friends find out the truth and side with Kouta instead of him. Mitsuzane's solution to this development? To ally himself with the resident Mad Scientist and shoot Kouta in the back while he's distracted. Although he fails to kill him, it gets worse from then on as he stands idly while his older brother is seemingly murdered, takes his Transformation Trinket and tries to commit first-degree murder on Kouta once more while keeping the façade that he is his brother Takatora, who Kouta befriended not too long ago, and acting like he's still Kouta's best friend whenever they meet untransformed. To top things off: After once more standing by and letting an ally get killed, even if that person was the Hate Sink of the series, he allies himself with Redyue, the resident Psychopathic Womanchild, and his acts get even more despicable. To the point that he's shown his true face to Kouta while trying to verbally break him and also beating him up untransformed. When Takatora shows up, still alive, and decides Mitsuzane needs to be stopped, they fight. Takatora hesitates in giving the coup de grace... Mitsuzane doesn't.
- 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.
- Once Upon a Time: Regina becomes increasingly dark and angry 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 "Because I loved it". And she still manages to remain good, despite this causing an addiction, and she refuses to obey Rumplestiltskin. Then, he gives her a Hope Spot 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.
- Revolution: Ever since Rachel Matheson made a deal with Randall Flynn to ensure Danny's survival from birth ("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 ("Chained Heat"). She turned herself into Miles's custody to allow her family to escape his clutches ("The Plague Dogs"). She apparently refused to reveal or do anything for 7 years...until Danny ends up in Monroe's custody ("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 save her own life and Danny's ("Kashmir"). She insists on destroying the pendants rather than letting Team Matheson use them. She pulls out a nanotech capsule from Danny's corpse ("The Stand"). She slapped Charlie where her daughter tried to call her out on leaving them all those years ago ("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 ("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 ("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 Danny. She is also willing to throw Aaron under the bus to achieve her revenge ("The Longest Day"). She has been sinking to new lows as the series goes on.
- Smallville: Lex Luthor has this happen to him over the course of this show, going from a 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'.
- An interesting example with Tony Soprano in The Sopranos. He starts the series as a Noble Demon who tries to run the mob in a manner in which few people will get hurt. However as the show progresses, Tony becomes increasingly desperate to hold onto the power he's gained. This, coupled with the numerous things he suffers, causes the standards he had to begin slipping away from him. By the series finale, he's effectively become a full-blown Villain Protagonist, albeit a self-aware one.
- Cho Sang-woo in Squid Game begins as a jerkish but well-meaning friend to protagonist Gi-hun, helping him and the team win through several games. By the fourth game however, he coldly betrays Ali, the man he called brother just so that he can wipe the debt against him, by the next game he is murdering allies just to get an edge in time, and before the final game he murders team-mate Sae-byeok just so that she and Gi-hun can't end the game early. The final game has him try to kill Gi-hun as well when he's down.
- Star Trek: Deep Space Nine: 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 Omnicidal Maniac.
- Afraid of the Dark by The Megas is about Shadow Man's terror as he slowly loses his old personality and his reprogramming takes over. Midway through the song, the darkness actually starts singing to him.
I feel it tearing me apartAre you afraid of the dark?I feel the shadow in my heartAre you afraid of the dark?
- Dr. Light goes through this for a while. His first song ("The Message from Dr. Light", on Get Equipped) is about his love and pride in his son, Mega Man. His second, on History Repeating (Blue), is about his growing hatred of Wily; that one's called "(I Wanna Be The One) To Watch You Die". (Luckily for everyone, Mega Man delivers a Kirk Summation in "I Refuse (To Believe)" that snaps him out of it.)
- "Weird Al" Yankovic plays this to ludicrous extremes in "Don't Download This Song", talking about where illegally downloading music can lead.
Cause you start off stealing songs,
Then you're robbing liquor stores,
And selling crack,
And running over school kids with your car!
- Deadlands uses this as part of the two most extreme 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 Gameplay and Story Integration, these are backed by mechanics that eventually determine when the player becomes invalid.
- In 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 Dark Lord in their own right. The more evil the act, the more likely that the Dark Powers will take notice, with some acts,— known as Acts of Ultimate Darkness— being so vile, heinous and cruel that they all but guarantee the Dark Powers' attention.
- The Chronicles of Darkness game lines all have a Karma Meter and take place in a Crapsack World rife with challenges that can threaten Morality degradation. Moreover, while Muggles can regain Morality for free through major acts of heroism, any supernatural Player Character has to spend precious Experience Points from the Point Build System to climb back up the slippery slope — and they have more ways to lose morality as well. This struggle is especially applicable to Vampire: The Requiem and Demon: The Descent, which emphasize the characters' conflict with their inner, amoral, inhuman natures.
- Pictured above: Big Boss from the Metal Gear series. In Metal Gear Solid 3: Snake Eater, he was an idealistic and patriotic spy for Cold War-era America, but the revelation that his mentor, The Boss, allowed herself to be branded as a traitor for the sake of national security begins to erode at his feelings of loyalty to his country, turning him into a Knight in Sour Armor come Metal Gear Solid: Peace Walker. Eventually, he and his former CO in FOX, Major Zero, come to an impasse on what they believed The Boss's will was: Zero believed The Boss wished for an end to war by means of a world ruled by a singular entity. Big Boss disagreed and, after breaking off from Zero when he learned he was being cloned, pursued his own vision of The Boss's will: a nation-state where soldiers were free from government control to fight as they wished — Outer Heaven, thus leading to the events of Metal Gear.
- A major theme in BioShock, where the two Big Bads during the backstory change from rude ruler to the people they hate most (in the first, an objectivist became first a dictator, then a totalitarian dictator, in the second, an Altruist became more and more selfish and ends up sacrificing everything to save herself). The lesson here is the danger of fanaticism.
- Can also apply to Subject Delta in BioShock 2. The "Lamb is watching" refers to Eleanor. And, sure, you do what you need to in order to get to Eleanor... but whatever you do, Eleanor will pick up from there. Harvest little Sisters? Kill NPCs? You watch in first person as Eleanor at the end of the game takes your lessons to heart.
- In Mafia: The City of Lost Heaven, Tommy starts off trashing a rival family's cars and finishes the game as a stone-cold killer.
- Arthas in Warcraft III is initially a Well-Intentioned Extremist when he decides to kill the citizens of Stratholme who ate infected grain which turns humans into zombies and would soon morph into the undead. After unwittingly selling his soul to the Lich King in order to make use of the sword called Frostmourne, 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 World of Warcraft, the war-mongering 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 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 witnessed the horrors of the afterlife (which include being slowly devoured by soul-drinkers as your senses fade to nothingness). 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. Shadowlands reveals she Jumped Off The Slippery Slope during her time in the afterlife by selling out to a God of Evil to send every dead soul in Azeroth to the soul drinkers, and her razing of Teldrassil cemented it. note The Shadowlands Expansion Pack would eventually reveal that Frostmourne stole the part of her soul that contained her morals, so she became more evil with each expansion,until she finally gets the Soul Fragment back at the end.
- Joshua Graham of Fallout: New Vegas began as translator and missionary, but slowly compromised himself until he became known as one of the cruelest, most dangerous men in the Mojave. He gets better, though.
- Graham does, however, subvert the trope in his actual in-game appearance: although he has long since slipped into evil and been reformed, the conflict of his character arc in-game is seeing whether he can stay on the path of righteousness, or whether his hatred and rage will ultimately drag him right back down the same path again.
- Spec Ops: The Line: Walker's entire character arc is one of these.
- In Baldur's Gate: Siege of Dragonspear, during the story it soon becomes apparent that this is what Caelar Argent is doing under the influence of her treacherous advisor Haerpanaan. While her goal is noble, her methods are anything but, and bring the Sword Coast to the brink of war. Right before the final battle, she has a Heel Realization, after which she can either decide to Then Let Me Be Evil or undergo a HeelFace Turn, depending on the player's actions.
- In Saints Row, the 3rd Street Saints start off as a small gang based in the Saints Row district who wish for a city with the other gangs erased from existence. After they achieved their goal, they become more like the very gangs they wanted gone. Julius Little, the founder of the gang, decides enough was enough, and (after getting arrested) attempts to kill his second-in-command (you) in a yacht bombing and go into hiding. Five years later, Julius would describe 3SS during that time period as "Vice Kings that wore purple".
- Dawn of War II: Chaos Rising: The Corruption mechanic makes squad members go through this, by giving them increased stats but also making them slip closer to Chaos, until the fateful level where whoever had the highest Corruption is revealed to be the traitor (canonically Avitus). The way you respond to certain objectives also adds Corruption, mostly by denying squadmates permission to join on missions here they have a personal stake. Corruption-reducing items are also available, but they also reduce your stats as penance, and while it's possible to go through the game with all your squads innocent, the role of traitor then falls to your Mission Control, Martellus.
- Undertale makes this part of The Reveal in Neutral route playthroughs: Your LV, or "LOVE", represents your "Level of Violence", your capacity to inflict harm, which increases as you accrue more EXP (or "Execution Points"). The higher your LV, the less inhibited you would be in harming others, which translates to increased damage against monsters. Thus, it's all too easy to develop an insatiable bloodlust the more you kill. Sans has things to say about this if your LV is higher than 1.
- In Book 9, Part V of Schlock Mercenary, 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.
- The inverse is discussed in The Order of the Stick, with Durkon noting that Good is as seductive as evil, when you get down to it. Notably, the person he's saying to, Belkar, is experiencing this himself.
Durkon: Ev'ryone always talks about tha seductive power o' Evil, but I think Good's just as slippery a slope. Doin' good - sometimes just seein' other people do good - feels good. Tha feelin' gets ta ye ev'ntually. Sometimes I think tha only reason more evil folks dinnae succumb ta it is tha it feels bad ta realize how bad ye've been. Most'd rather pretend ta nev'r feel nuthin' than experience tha pain.
- In Dr. Horrible's Sing-Along Blog, Dr. Horrible starts off as an ineffectual Anti-Villain, maybe with good intentions, but through constant humiliation, losing his love interest to the Jerkass Smug Super Captain Hammer, his own urge to join the Evil League of Evil, and the League's threat that he 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 which ends up killing Penny instead.
- Blake describes this happening to Adam Taurus, her former partner from the White Fang. At first, when he killed someone, they were accidents, which soon became acts of self-defense, and by the time of the Blake Trailer, Adam was killing (or trying to kill) people out of spite. While her initial claims are suspect given her own bias, RWBY: Amity Arena would reveal he legitimately was an idealistic young boy once who wanted equality, but that all changed after he was horrifically branded on his face and eye, which led him to wanting to get back at humans for Faunus. The Volume 6 Character Short shows that his first kill, done to protect the original High Leader Ghira from a racist human, was made in a fit of battle passion after he non-lethally subdued the other human attackers. While he did show some shame over it, he was more surprised when Sienna, Ghira's eventual usurper, applauded his actions. It's strongly implied that Sienna enabled his violent tendencies without realizing he was becoming more motivated by power than by helping Faunus.
- James Ironwood initially started the series being a member of the Benevolent Conspiracy committed to fighting the evil plaguing the world. However, as time goes on and he suffers more defeats and trauma, he slowly begins taking more ruthless and extreme actions, becoming He Who Fights Monsters. At one point he expresses his belief that Salem's greatest advantage was her own Lack of Empathy. By the end of Volume 7, he has no problem murdering any who dispute his methods, and by the tail end of Volume 8, he goes so far as to threaten to blow up a city. Word of God is that Ironwood's fall to the dark side was supposed to seem slow and natural.
- While the morality of Dark Magic in The Dragon Prince depends on what side of the continental divide you live on (humans tolerate it since it's the only apparent way they can use magic, while elves and dragons see it as an abomination), most of its practitioners start using it for larger and more monstrous spells the longer they have access to it. Viren initially used it for the greater good, sacrificing the heart of a rock titan to save his nation from a famine, but by season 3 he was using Dark Magic to forcibly upgrade innocent soldiers into monsters to give him an opening to kill the titular Dragon Prince, a hatchling, for no other reason than he wanted to use the Dragon Prince as a power booster.
- Catra in She-Ra and the Princesses of Power starts out as a villain, but comes across as more indifferent to the consequences of her action than outright malevolent, and she retains sympathetic characters given her Freudian Excuse and complicated relationship with Adora. Unfortunately, her out-of-control jealousy of Adora and inability to process her emotions constructively lead to her becoming steadily worse: going from trying to recover Adora to trying to kill her in order to move out from under her shadow, getting crueler and more selfish, and eventually trying to destroy the world rather than give Adora another victory.
- Star Wars: The Clone Wars:
- While Kit Fisto downplays it when talking to the other Jedi Council members about his former Padawan Nahdar Vebb's demise, it is quite clear throughout "Lair of Grievous" that Nahdar's pride and growing anger, frustration and desire for revenge had him teetering on falling to the Dark Side by the time Grievous killed him.
- Anakin Skywalker undergoes this throughout the series. As the seasons wear on, he slowly becomes more ruthless and willing to Pay Evil unto Evil. All part of Palpatine's plan, of course, since he wants Anakin as his next Sith apprentice.
- Reagan Ridley from Inside Job gets accused of this, to be fair a Mad Scientist attaching four robotic limbs to their back is a very bad sign.
- Then there's the time she wanted to break up with a guy gently because she wanted to, in her words "avoid being the bad guy", it doesn't work out.
- Varian from Tangled: The Series did this as season 1 progressed. While he started out as an ally to Rapunzel who usually only caused harm to others through complete accidents, after his father got encased in crystal and Rapunzel was unable to help him, he completely snapped. The last time we see him that season, he's being hauled off to jail for several counts of high treason and making an attempt on the lives of Queen Arianna and Cass, still convinced that none of his actions was his own fault, although not without reason...