Johan Liebert of Monster indulges in this trope on more than one occasion. He's hardly ever shown as anything other than an awful psychopath who enjoys murdering people for little more than shits and giggles. However, during the university arc, we see him lovingly playing with children, and helping an old man and his illegitimate son reunite for the first time. However, this is quickly subverted when we see that he manipulated said children into playing a game by which they would attempt to balance themselves on the sides of rooftops, whereby many children fell to their deaths, and that he merely brought the father and son together so that it would be easier to kill them both (he fails on the second part, but still). He also gives money to a sickly homeless woman... because he can tell she's a heroin addict, and would almost certainly spend the money to buy more.
The first one involves a man who is first introduced as a Chivalrous Pervert with an odd sense of humor, then turns out to be a rapist assassin with a gun that fires spiked balls dosed in extremely painful toxins.
A chapter ending introduces a few techs at the Diclonius research facility, along with their boss, a quirky, joking bishonen with a fondness for candy sticks. All is well and good... until a Reveal Shot reveals that they're working, joking and laughing in an office with a window showing an endless train of mutilated and uncensored Diclonii torsos for that radar system rattling past.
In the first episode of Code Geass, Prince Clovis is introduced giving a powerful speech condemning an act of terrorism by the Japanese resistance which seems pretty conciliatory, as he underscores how loyal Japanese are equal citizens of Britannia. Then a moment later, he is shown going back to socialize at a party, demonstrating that all of that pathos was a put-on. By the end of the episode, he shows his True Colors as a neurotic nutjob, by despairing due to C.C's escape to the point of ordering a murderous pogrom on the Japanese ghetto to cover it up. Unlike many of these examples though, Karma catches up with him quickly so he doesn't make it very long in the series.
Clovis's older brother, Prince Schneizel, was kind of the same. He was introduced as a seemingly nice guy who many fans speculated was a heroic Anti-Villain in contrast to Lelouch, a ruthless Anti-Hero. Then, he starts manipulating the mentally unbalanced TV Genius Nina into building a nuclear weapon, uses a critical momentary absence of Lelouch to turn the Black Knights against said leader, and eventually reveals his plan to nuke millions of people and declare himself God. And using his half-sister Nunnally, also very unstable at the moment, to such an end. Of course, there was at least one sign prior to this: his smile as the Avalon prepared to nuke both Suzaku and a pinned-down Zero in the first season.
In Fullmetal Alchemist; While we see fairly early on that the Amestrian military is a fairly ruthless and potentially dodgy organization, its leader, Fuhrer President Bradley, presents himself (despite his title and kickass fighting skills) as a more-or-less benign individual who does what he thinks is best for his country and his beloved family. He even offers to help our heroes fight the conspiracy inside the military. Then it's revealed that he's a homunculus and part of the aforementioned conspiracy, not to mention the one who ordered the Ishval civil war and subsequent genocide campaign. Despite this, he's among the most human (not necessarily sympathetic) of the homunculi and it seems that his love for his wife, in the manga at any rate, is genuine.
To add to that, Bradley is shown to be shaking during Hughes' funeral, one of the major Tear Jerkers of the series. When Mustang brings this event up, it is revealed that he was in fact shaking with anger at the noise that Hughes' daughter Elicia was causing, as she cried over her father being buried.
Amazingly, the series manages to one-up this. Selim Bradley is a cute little kid who looks up to his father, studies hard so he help the country when he grows up and fanboys other characters with big sparkly eyes. Which makes it all the more horrifying when the reader learns that not only is he a homunculus, but the oldest of the second-generation homunculi and arguably the most powerful and evil. His power is a living shadow that tore a group of Briggs soldiers to pieces and left the survivors so traumatized that they were almost insane. Worst of all, his poor mother has no idea that her family are evil homonculi (although they both seem to care about her in their own ways).
In One Piece, Marshall D. Teach aka Blackbeard, our story's likely true Big Bad first started out as a rather jolly Boisterous Bruiser and at least Affably Evil type, always encouraging Luffy to get stronger, caring for his crewmates, etc. Then fast-forward to the Maineford Arc, where he mocks Whitebeard, feigns sympathy with him, then gleefully and brutally murders the old man who he once called father for well over 20 years plus with his crewmates, then steals his Devil's Fruit, revealing himself to be always just a power-hungry megalomaniac. And it's likely this won't be the first thing he does like this, before and after either.
See also, Eustace Kid, at first presented as being disgusted with the World Government Slave Auctions and setting himself up as a worthy opponent to Luffy and Trafalgar Law. Roughly a hundred chapters later he's seen crucifying pirates attempting to flee the ludicrously dangerous sea of the New World.
Word of God is that the only reason Kid's bounty was higher than Luffy's is that Kid leaves a trail of corpses wherever he goes. When he said that he kills anybody who laughs at his dreams, he's not joking.
While all of his acts of horrific violence have been off screen, its becoming more and more obvious that Trafalgar Law himself isn't the mellow pretty boy he acts. This trope hasn't been played straight as of yet, but as of chapter 659 he sent the hearts of 100 pirates to the world government to become a Warlord of the Sea. Later it is revealed by his power, these hearts are still beating and the people who lose them are still alive but now at the mercy of the one who holds their heart. Crush the heart and they die. No word on how many of the hundred victims are still alive. It's also worth noting that in his first appearance, the other Supernovas were as wary of him as they were of Kidd.
Completely inverted with Jinbe. When we first heard of Jinbe, being Arlong's former captain and the one who let Arlong run wild in East Blue, it seems like Oda was setting Jinbe up to be a major villain. Who would have thought that he would actually be a honorable and a decent person, become one of the Straw Hats' biggest allies but also be invited by Luffy to join the crew?
Darker Than Black does this in the new season with the team of Japanese agents. While immediately established as antagonist's to Hei, this isn't really a strike against them for sympathy points, given the Grey and Gray Morality of the series. Mina is a Bad Ass fighter and provides lesbianism and Genma is highly affable and funny and seems to be a Lovable Sex Maniac. Then, in the third episode, you have them ambushing a squad of Russian soldiers. Genma hijacks a train and as he uses it to kill, you see the mangled body of the conductor next to him. Then, after Mina shows up and slaughters several more soldiers, Gemna creates a gas explosion to kill the remainder and during this whole time, finds this carnage absolutely hilarious. This is shockingly violent, even for Contractors and conveys total lack of empathy for human life. Finally, while Genma initially seems to be a Lovable Sex Maniac, he's really more like a pedophile.
There's also the token human, Yoko. "Look at me, I'm all shy and glasses-y and Moe Moe! A girl kissed me and I liked it!" Then boom. She DePowers Hei PAINFULLY and seems absolutely thrilled by it, like he's a guinea pig as opposed to a person. Not to mention Episode 6, when she starts pulling Scary Shiny Glasses and generally looking like Gendo Ikari was reincarnated as an early twenty-something year old girl.
Izaya Orihara in Durarara!! is introduced acting like a nice guy and seems to be comforting a troubled girl named Rio Kamichika. Then, it turns out that he had persuaded Rio into a Suicide Pact, and he tells her that all the nice things he said was just him screwing with her, which pushes poor Rio to really attempt suicide (she survives unharmed, but no thanks to him). After this scene, he is generally more comically evil, but the show has moments once in a while to remind you what a creepy, sociopathic person Izaya is.
He was trying to make a point that her suicide would be pointless because she's not so different from everybody else that has problems and told her to think about it for a minute. Of course, he wouldn't care if she did jump because it was her decision.
In Bleach,, Aizen's a pretty nice guy right up until he stabs Hinamori.
Puella Magi Madoka Magica has Kyubey. He looked innocent and overall the typical mascot pet, though with something sinister about him, until Episode 6 reveals really nasty things about him.
Yukiteru's dad from Mirai Nikki. At first, he looked like a genuinely nice person who was just trying to help his son. Then it is revealed that he is trying to find and destroy Yukiteru's cellphone- Therefore killing him- To erase his debt.
Though in his defense, he was not aware that destroying his son's phone would kill him.
Sabertooth as a whole gets this in Fairy Tail. Initially just the strongest guild that Fairy Tail must compete with, full of members who have all sorts of cool powers. Then we see exactly how they deal with failure. Special mention goes to Sting, who was introduced as a new dragon slayer who was once a fan of the main character, and is far more interactive than his companion Rogue. After Sabertooth's collective bait the dog moment Sting is seen laughing at the misfortune of the girl they booted out (this despite his having failed worse than her and gotten off with a warning) and claiming she deserved it for being weak while Rogue insists that as a guild they ought to look out for their members.
In the Ace Attorney manga, Robin Wolfe is polite and friendly toward Phoenix when Phoenix comes to defend him when he is about to be accused of killing his employee Eddie Johnson, but increasingly suspicious hints pop up about him. His wife is cold and distant toward him, his daughter pokes holes in his claims about Eddie, and Eddie's brother confronts him about his role in Eddie's death. While Robin denies his brother Bobby's existence, the "Den of Spiders" built and maintained at considerable expense, seems to be a Pet the Dog moment as does his having him run an errand near the time of Eddie's death, but then Phoenix sees that the Den of Spiders has a chair with restraints that is used on Bobby to keep him out of sight of guests. By the end of the night, Phoenix and Maya are essentially convinced Robin drove Eddie to his suicide... and around this, time Robingetskilled.
In the Investigations manga, Chase Clink seems like a friendly and reasonable police chief, until Emi St. Cloud is murdered and he suspects Shawn Southern. When Edgeworth protests his haste in declaring Shawn the suspect, Chase derides him for spending so much time around Gumshoe. Chase is also the actual murderer, who killed Emi St. Cloud and had Shawn framed in order to cover up a secret that he thought would sully the police department's name.
In Naruto, Mizuki's first line is suggesting that Iruka let Naruto pass despite not being able to make clones, a suggestion Iruka shoots down. Soon afterward, he has a talk with the depressed Naruto, trying to get him to understand why Iruka is as strict as he is. He then offers an alternative way for Naruto to graduate- all part of his plan to steal the scroll of forbidden jutsus.
In Mai Otome, Tomoe initially seems fairly humble about being the second ranked student in Garderobe and welcoming toward Arika, in contrast to the top-ranked Nina, who says she only sees her classmates as rivals. When Arika's uniform goes missing and she's suspected of selling it, Tomoe seems unwilling to believe that it's the case. Then comes the scene when Tomoe berates the girl she bullied into stealing the uniform for deviating from the plan and slaps her, and Tomoe goes downhill from there.
In the manga for A Certain Scientific Railgun we're introduced to the scientists in charge of the Sisters/Level 6 development project. They're friendly, affable, serve one of the Misaka clones an expensive tea and chat with her... and then without missing a beat they ask her to clean up the corpses of half a dozen of her brutally killed sisters. Those who have read or watched Index before Railgun will probably see it coming, but for first time readers it's quite the shock.
The Joker does this a lot. As one comic writer said, "The Joker's job is to make the audience laugh, then feel ashamed about it afterwards."
In a 2006 Captain AmericaWhat If? story, Steve Rogers is a soldier during the Civil War era, part of a group ordered to attack some American Indians. When he expresses doubt about this, his superior officer Colonel "Bucky" Barnes appears to understand. Later, it's shown that the Colonel not only allows the attack to happen, but in fact has his men surrender the loot to him as well.
One of the longest-term and most emotionally powerful examples was Cassidy in Preacher: he was a Lovable Rogue for practically the whole first half of the story, but the second half was devoted to a very unpleasant Face-Heel Turn coupled with increasingly grotesque and horrific revelations about his past actions.
Quentin Tarantino admits to doing this with Mr Blond in Reservoir Dogs, whose Moral Event Horizon moment involved cutting off a cop's ear and slicing his face while he was gagged and duct-taped to a chair, then dousing him with gasoline and preparing to set him on fire before he was stopped. All of this is done after we get introduced via a little How We Got Here flashback and get to see him do the twist to some funky 70's music on the radio. This also applies to a lesser extent to characters like Mr. White and Mr. Pink, who seem quite sympathetic and ineffectual, until in flashbacks we see them shooting up cops. However, they remain sympathetic characters, so they don't really fit this trope.
And again in Jackie Brown, we assume we're on Samuel L. Jackson's side, because he seems pretty much like his character in Pulp Fiction, with some funny lines about AK-47's and a stoner girlfriend, etc. He goes on to shoot or threaten to shoot most of the characters in the movie. Robert De Niro's character is pretty much the same, except we don't find out until much later on when he shoots his/Ardell's girlfriend dead because she wouldn't stop talking.
Maman in Slumdog Millionaire. A viewer might be slightly suspicious when this man is offering homeless children soda and giving them a home in an orphanage. You may think he's a little shady, but not too terrible when he has the children panhandle in exchange for food and board. Then when he really likes you, you get to sing for him. However, he has a way to make every singing orphan worth double.
Barton Fink. Charlie seems like a lovable oaf and becomes Barton's only real friend. Then it turns out he's a homicidal maniac who probably killed his girlfriend and gave her head to him in box.
The Imaginarium of Doctor Parnassus brings us Tony. He's introduced as a likeable chap who has a gift for bringing people in to be enlightened in the titular imaginarium. It's shown that he was involved in some sort of scandal about a children's charity, but he still comes off as a Loveable Rogue. Then it's revealed that he was selling the children's organs on the black market. The man triggers an Even Evil Has Standards reaction in the Devil himself.
Done deliberately with the film version of Secret Window - according to the director, by the time our protagonist finally snaps completely and kills his ex-wife and her boyfriend, we were meant to be too involved with him to stop cheering him on.
Any horror film where they don't show who the killer is before the big reveal. Especially in the Scream film series where Ghostface turns out to be someone you wouldn't expect to be a homicidal mass murderer.
A subtle example in Watchmen. There's a Male Gaze shot of Silk Spectre in her form-fitting costume, then a cut to the Comedian leering at her. He's a cool superhero type, and he's also just a guy like us! Then, moments later, he tries to rape her.
In X2: X-Men United, Magneto and the Brotherhood team up with the X-Men in an Enemy Mine battle against a racist, genocidal military colonel. Magneto's more or less leading a rescue mission to save Professor Xavier, and the two teams fight together so well (the movie's even subtitled "X-Men United") that you can't help but cheer him on and start to wonder if, all things considered, he's really such a bad guy. And then he proceeds to remind the audience that yes, he really is a villain, when instead rescuing him, he tries to use the captive, brainwashed Xavier to kill every non-mutant on Earth.
In Dragonheart we first see Einon as though he is like any other fantasy hero, who was given Draco's heart and the audience assumes it would be about a A Boy and His X. But in a few minutes, he is in fact a spoiled prince who is becoming more oppressive and cruel when he force the rebels into building his new castle, had their leader blinded.
Though the signs were present long before that. It was infact the moment he cam upon his dying father, and tried to steal his crown that got him injured badly enough to need a dragon heart transplant in the first place.
The robber in The Amazing Spider-Man is introduced to us this way. He's behind Peter in line at a convenience store, who is trying to buy a chocolate milk and is two cents short. The jerkass clerk won't even let him make up the difference from the "take a penny/leave a penny" jar because he hasn't paid enough. As Peter leaves, the robber tosses his money on the floor, making the clerk bend down to get it, empties the register while he is distracted, and tosses Peter the milk. Since the robbery was non-violent, the robber was nice to Peter, and the clerk was a jerk, you are tempted to like the guy and understand why Peter doesn't stop him. Moments later he has murdered Uncle Ben for getting in his way.
The Japanese horror classic Audition perfectly fits this trope.
The film Side Effects proves to be this with the main female protagonist Emily. The film seems like it's a cautionary tale about the dangers of prescription medicine with Emily being the tragic victim. Only to reveal that she used prescription drugs as cover to kill her husband, set up her psychiatrist to take the blame, and get rich off the stock market.
Annie Wilkes in Misery. She saves the author Paul Sheldon from a deadly car crash in the middle of a blizzard. She makes it clear to be a huge fan of his books. She seems dedicated and delighted to nurse his wounds until he makes a full recovery. Though she almost violently disagrees with Sheldon's new book, it's just the actions of a passionate fan. Nothing wrong with that, right? Too bad she's revealed to be a psychopath that has no intention of letting Sheldon go or let anyone know he's still alive. Then it's revealed that she had a dark past where she poisoned her husband and was a nurse who poisoned many of her patients.
Pan's Labyrinth: Captain Vidal is introduced as a stern militant, with a dash of My Country, Right or Wrong to go along with his fascism. He's polite to Carmen and stern to Ofelia. When he finds a couple of hunters who his men have captured, he searches their bags, finding some tobacco and a beer bottle. He shushes them whenever they talk, and when the younger hunter insists that the other, his father is telling the truth, Vidal calmly walks up to him and beats his face in with the beer bottle. Then he shoots the man's father (not even bothering to warn the soldier who was standing right behind the man, who could have been killed by the exit wound if he hadn't moved away), and calmly shoots the first hunter. He later finds that they were only hunters, and tells his men to do a better job of searching before they bring people to him.
Mr. Teatime in Hogfather is introduced with a Badass sequence in which he sneaks into the head assassin's office, then turns out to be a total psycho.
Of course, we only get a couple paragraphs of "what a badass" before "Oh my Om, what a psycho" sets in, because we first see him playing with some dogs; the character speaking to him expresses surprise, because on his last job he nailed one to the ceiling.
Wilkie Collins did this in his novel The Woman in White with Enigmatic Minion Count Fosco. Fosco is so friendly and charming that the heroines turn to him for help against the seemingly main villain, Sir Percival Glyde, who is a Dastardly Whiplash type. Turns out that Fosco is actually a master villain who is aiding Glyde. It's also shown that Fosco has cowed and abused his wife into becoming a Stepford Smiler and it has been argued by British critic John Sutherland that the discrepancies in time between what Fosco says it took for Anne Catherick's death and what another character reports is meant to suggest that Fosco killed her after a prolonged period of torture and rape.
In the Warhammer novel Inheritance, the character of Vlad von Carstein is introduced like a non-annoying version of an Anne Rice vampire, who practically sweats pure liquid awesome. He's philosophically inclined, a good fighter, looks cool, enters like a true badass, and ohmigod did he just slaughter hundreds of people in extremely sadistic manners and resurrect them as zombies?
In George P. Pelecanos' novel King Suckerman, ex-con Wilton Cooper appears to be a cool Badass but is gradually revealed to be a rather frightening sociopath.
When introduced in the first Gormenghast novel, Titus Groan, Steerpike is not only the most dynamic character in the entire cast, with a clear and sympathetic goal (escape), but is the viewpoint character for most of the book, not to mention showing extreme skill at what he does. By the time he reveals himself to be a deceitful serial killer, the reader has been well and truly disposed to view him as the hero.
In R.L. Stein's Fear Games trilogy (Part of The Nightmare Room), the sorceress who is the trilogy's Big Bad lures a seagull to her hand, pets it while she tells it her evil plot, then snaps the seagull's neck and throws it to the ground.
In the Dale Brown book Air Battle Force, General Gryzlov first appears as A Father to His Men, chatting with the aircrew of the bomber he's on. Then it turns out that he's there to oversee firebombing the shit out of Chechens.
Ventrue can only drink from a certain type of person. Jan Pieterzoon is a decent guy who happens to be a vampire, thrust into a bad position and doing the best he can. We even see him mourn for his aides when they die, which lasts until he decides that he needs a new source of blood: Jan can only feed on rape victims, so he Dominates the night manager into raping the check-in girl so Jan can feed. But Jan feels bad about it, so it's okay... ?
Not that it excuses it at all, but Jan was so badly damaged, he needed to feed right off or he wouldn't have lasted the night.
24: Since revealed to be alive, Tony Almeida's been acting a little shady, but also has been doing everything in his power to aid Jack and the FBI stop the Starkwood conspiracy and destroy their bioweapon which has already infected Jack, personally taking out the main facility. Then someone escapes with a sample of the weapon and Tony teams up with FBI head agent Larry Moss to take him down. But when they corner the guy and Larry is shot, Tony then proceeds to suffocate him to death and reveal he's working with the man who has the sample.
Battlestar Galactica (Reimagined): Happens a few times on the new show. First there's Cavil/#1, who's introduced as a Deadpan Snarker type and even seems to be one of the more sympathetic Cylons. As the story develops, we get to know Cavil for what he really is. Then there's Tory, who learns she's a Cylon, but manages to keep it together at first. When Cally has a breakdown upon realizing her husband Tyrol is a Cylon, she takes her infant son and prepares to toss herself and him out of an airlock. Tory shows up, talks Cally down-and then takes Cally's son before ejecting her into space anyway.
Firefly: Had a good example with Bounty Hunter Jubal Early. It's clear that Whedon assumed that viewers would react to him with similar good will as was shown towards Boba Fett in Star Wars, and when he first appears, he is an erudite and funny Bad Ass. Then he starts threatening to rape Kaylee and admitting to his love of torturing animals as a child.
Game of Thrones: Joffery Baratheon proves to be this. He starts off as a bratty, spoiled, prince that gets humbled and learned his lesson. He seems to get better and make an effort to be the kind of prince that would make a good king. Only to reveal his true colors after he becomes king. He has Ned Stark beheaded for treason, despite seemingly promising Sansa Stark, his fiancee and Ned's daughter, as well as his own mother, that he would spare him. He then goes on to mentally and physically torment Sansa and others at court. And once he gets his crossbow....
Hannibal: The title character is a ruthless, cannibalistic serial killer, but in every other capacity he's thoroughly helpful, polite and very entertaining, not to mention an excellent chef and a great host. Then he discovers that Will has severe encephalitis, starts slowly Gaslighting him so he has a front-row seat to a mental collapse, and eventually frames Will as a serial killer. The only thing more dramatic than how quickly Will went from sane to insane is how quickly the fandom's opinion of Hannibal went from Draco in Leather Pants to evil.
LOST: Has Locke's father, Anthony Cooper. At first, he seems happy to finally meet Locke and starts giving him the family life he never had. Then it turns out all that was a con to steal Locke's kidney, after which he wants nothing more to do with his son. Later, he tries to kill Locke by pushing him out a window, which led to Locke ending up in a wheelchair.
Merlin: Morgause at first simply seems to be a Well-Intentioned Extremist who wants Uther off the throne for the good of the people. Her first two attempts involve telling Arthur the truth about his parentage and putting all the residents of Camelot to sleep without hurting them and she removes the spell to save her sister's life. But in season 3 we see how much of a villain she really is as she tries to drive Uther mad and get armies to invade Camelot. We also see her sadistic side through her treatment of Gwen and Cenred. And to boot she corrupts Morgana and turns her into the series' Big Bad.
Once Upon a Time: Greg Mendell, who appeared to be an innocent, likeable Muggle. Then it was revealed he actually had a tragic history with Storybrooke which led to him losing his father, and he became very sympathetic to fans. But then he was revealed as a Knight Templar who seems more interested in eradicating magic than finding/avenging his father, and is willing to resort to Cold-Blooded Torture and even mass murder to accomplish this.
Person of Interest: Elias helps Reese save an infant, only to lock Reese and the child in a refrigerated truck to force Reese's assistance.
Revolution: Throughout the first season, Tom Neville has been that sort of villain who just follows orders and doesn't seem to have anything personal with the protagonists. Then he defects from the Monroe Republic to the Georgia Federation. Then he's working with the protagonists to stop his former boss, Sebastian Monroe. Then he exploits the fact that Monroe is terrible at being a leader to get himself put in charge of the Monroe Republic. Now, you might think that the situation will improve. However, first he tells Monroe loyalist Captain Mark Franklin that he'll be let go...and then murders him in cold blood and makes it look like self-defence. Then he promises his son Jason that he'll keep Charlie and Rachel alive...but then decides to have the protagonists all killed off anyway. A lot of sympathy for the character is gone by the first season finale.
Samurai Sentai Shinkenger: There's Fuwa Juzou, who is a half-Gedoushuu and sets himself up as Takeru'sWorthy Opponent, constantly seeking to fight him. With him not really getting along with the head honcho of Gedoushuu, Chimatsuri Doukokuu, plus building up some 'friendship' with Usukawa Dayuu and the fact that he's half-human makes people think that since this is Super Sentai, he'd at least be shown as either a Noble Demon, or pull a Heel-Face Turn later. Then, he foils Akumaro's plan...by revealing that he revels on his Gedoushuu lineage, preferring to be a full-blooded Gedoushuu (which he did), and his sword Uramasa turned out to be his parents begging him to stop killing, but he doesn't care one bit, liking his profession as a Blood Knight to the max and wants nothing more than kill and more killing. At that point, any hopes of him as mentioned above are dashed forever and he places himself as one of Super Sentai's monsters.
Star Trek: Deep Space Nine: Actually an Invoked Trope when the writers thought that the recurring villain Dukat who, despite his charming demeanor and the fact that he somewhat cared for his illegitimate daughter was a hypocritical, crazed, sexually voracious dictator who sent millions of people to die in labor camps and didn't hesitate to sell his own people to the Dominion which directly lead to his home planet winding up thoroughly demolished by the end of the show, was getting too popular with the audience - the episode "Waltz" exists for the sake of showing the audience that, charm or no charm, this man is a monster.
Torchwood: Captain John, who is So. Cool...and kills people for no particular reason. This is done on his first appearance in the show.
Chiron and Demetrius in Titus Andronicus. They're introduced as a couple of thick comedic teenagers fighting over some girl; ten minutes with The Chessmaster Aaron and they go on to rape and mutilate her.
Though this was far from M. Hugo's original intent, the musical of Les Misérables gives its most upbeat, funniest, and catchiest musical number to Monsieur Thenardier and his wife, as they swindle, cheat, and serve questionable food to the patrons at their inn, and abuse and starve the little girl they're supposed to be taking care of. Watch and see if you can keep your feet from tapping.
Not even the rest of the cast is able to sit still!
Caesar's Legion in Fallout: New Vegas initally seem like a subversion. Their atrocties and reputation as powerful but mindless savages trying to topple civilisation seems to be their one defining attribute - until you meet Caesar himself and find out that he's a well spoken philosopher who wants to create a civilisation that won't implode on itself. But just annoy him a little and it turns out the Legion are every bit as self interested and nightmarish as their reputation suggested, endorsing everything from cannibalism, human sacrifice to rape. And just to kill any doubt that Caesar only sees this as a harsh necessity, he orders the peaceful town of New Canaan to be wiped out purely to torment his former Legate.
Kazuya Mishima of the Tekken franchise (and his evil 'alter ego' Devil) qualifies. Starting out the series with white clothing and somehow 'stoic' attitude, you'd think he's like The Hero, trying to topple his evil father Heihachi's company. Upon victorious, it is widely thought that he'd strive to steer his father's company to the righteous way. Cue the sequel, it turns out he does things far worse than Heihachi ever did, turning into a full-blown villain (with some minor things like being attracted to Jun Kazama, and having Angel), and has remained that way until now. You could actually get a hint of Kazuya's evil side since Tekken 1 if you buy the Playstation port, whereas he got Devil as his alternate costume.
Tekken 6 seemingly repeated this on Kazuya's son Jin. However, his Face-Heel Turn turns out to be his Batman Gambit to awaken Azazel and destroy it with his cursed bloodline, subverting the trope ultimately.
In the opening cinema of Blizzard's World of Warcraft Burning Crusade expansion, you see a rather beautiful Blood Elf woman playing with a creature made primarily of mana in a graceful, Disney-Princess kind of way... and after about 8 seconds of this she forcibly drains the things essence out, killing it. To be fair, mana wyrms are considered pests, but she does look rather sinister.
(Aside from his flashback appearance) Kefka from Final Fantasy VI is introduced in the story as a quirky and colorful Villainous Harlequin like character, humorously demanding that his shoes be emptied of sand in the middle of a desert and generally acting like a goofy manchild. He later reveals himself as a sociopath whose idea of fun generally revolves around mass genocide.
Yunalesca of Final Fantasy X is known as the first summoner to defeat Sin and save the world (albeit temporarily). She waits in Zanarkand as a ghost to greet summoners at the end of their pilgrimage. Until we discover she turns one of the summoner's guardians into a living statue forever and that she knows it's impossible to truly defeat Sin this way. When the protagonists refuse to go along with her, she does NOT take it well. And shockingly, she actually remains an Anti-Villain the whole time.
Subverted with Slayer in Guilty Gear XX. One of his intro sequences features him with an attractive woman clinging to him... who he then drains of blood until she's nothing but an empty husk. This seems like a straight application of the trope... until you get into the series story. The woman in question is his wife, who has the special ability that she simply can't die, period. She kills parasites and disease-causing organisms just by being near them — to the point Eddie (a body-stealing bioweapon) tries to possess her in one of his endings and melts — and being drained like this is, at worst, a minor inconvenience for her. Slayer is a villain by some readings (he's not just an assassin, he's the founder and former head of the guild), but his relationship with his wife is one of his better aspects.
However, he aspires to become like Litchi in his story mode ending in Continuum Shift.
Which is, kind of subverted later, when people are introduced to Litchi, she displayed herself as a kind hearted woman who cared about everyone and would even sacrifice herself to save someone unknown as Carl at that time. Time by time, we are also told that she was trying to save her lover. Come Continuum Shift, however, said emotion became a catalyst for her to do a Face-Heel Turn, joining in Carl's father for a chance to save her lover, maybe to establish that she is not meant to be the sensible Love You and EverybodyMessianic Archetype, but a desperate lover to the level of near-obsession. Somehow she still retained her kind self, but it was probably a type of baiting provided by Arc System Works.
In the first game, there's that mild-mannered informant Hazama who merrily helped Noel... until suddenly in the True End, he reveals his true card, that being Troll extraordinary Terumi Yuuki, who's responsible for nearly every single depravity done to the world.
Dimitri Rascalov in Grand Theft Auto IV. At first, he seems like a decent guy, especially when compared to his boss, Mikhail Faustin. When he orders Niko to kill Mikhail, most players would think he's doing it for the right reasons. However, he then betrays Niko to Ray Bulgarin, a human trafficker he ows money to, and becomes one half of the game's Big Bad Duumvirate. And he later tries to make Niko's life hell with a series of progressively escalating Kick the Dog moments.
Arthas Menethil in Warcraft. While he's first seen, he may seem to be a genuinely good person given a lot of shits to the point his desire to save his country makes him do a Face-Heel Turn and eventually gets promoted into the Big Bad. It wasn't later that supplemental materials reveal that he's not as goody-goody as his debut game pre-insanity showed him to be.
Eva Beatrice in Umineko no Naku Koro ni is introduced with a happy, innocent sounding tune and just seems so thrilled about her recent 'promotion' that even Battler applauds her. However, she turns out to be far worse than even Beatrice and disgusts an actual demon with her antics.
Inverted and played straight for different characters in Muramasa: The Demon Blade. In Momohime's storyline, we're soon introduced to a seemingly utterly vile Villain Protagonist by the name of Jinkuro, and a seemingly noble monk who helped save Momohime and seems committed to making Jinkuro pay for his crimes... but it quickly turns out that things aren't quite so black and white. Rankai, the monk, is actually just motivated by vengeance and will do anything to see Jinkuro die, including selling Momohime's soul to a demon, while Jinkuro, although still very much a villain, isn't quite as callous and devoid of redeeming features as he first appears.
In Penumbra: Black Plague Clarence initially seems to be a harmless and funny, if somewhat crazy character (a bit like Overture's Red). However, when he finds out he can make Philip hallucinate and uses that power to play "hilarious japes", which begin with causing Philip to see enemies from overture and culminate in tricking him into killing the Amabel Swanson, the one person who has been really nice to him in the whole game, he suddenly becomes a lot more sinister.
The Jagermonsters in Girl Genius often come across as goofy eccentrics who like drinking and fighting a bit more than normal guys...so sometimes it's easy to forget that they're hyperefficient killing machines who are only as moral as their master (so it's okay to root for them now, but you'd better hope Agatha's kids are more like their grandparents than their great grandparents).
Jagerkin are borderline example, as they're still likeable — extremely dangerous, but honorable Blood Knight bunch. Loud, love fighting, but not malicious at all — they readily admire foes who bested them and tend to ignore non-combatants altogether. And are loyal above all else.
And again with Eridan. The entire comic builds him up as a worthless Butt Monkey whose attempts at world domination are overly ambitious and doomed to failure, leading everyone to believe that he's an Ineffectual Sympathetic Villain (even having a quote from his introductory exposition on that trope page). Then he announces he plans to betray his friends and join Jack Noir, we learn that he committed genocide on the inhabitants of his planet after he murdered a few for no reason, and he proceeds to beat up Sollux for being in his way and murder both his love interest and the one person whom he referred to as a friend.
Doc Scratch is presented as a fairly polite villian who wants to help the protagonists (to further his own ambitions), and is even kind to Spades Slick, who spent his time at Scratch's pad trying to light it on fire and attack the host. Towards the end of his narrative, we discover an Awful Truth: he's kidnapped and abused Aradia's ancestor to the point where she becomes a BrainwashedDeath Seeker. This is best exemplified when he temporarily takes away her ability to breathe. Damn.
Not to mention Caliborn. Not long after his introduction, he aggressively solicits Dirk to draw him some pornography - surrealistic depictions of human courtship, with no nudity. His odd personality and over-the-top crudeness lead you to believe he's going to be a CloudcuckoolanderJerkass... then he reveals that he killed his sister by proxy. Laughing maniacally all the while. Also, he's Lord English.
And Redcloak at first appears to merely be Xykon's Deadpan SnarkerBeleaguered Assistant. Turns out he and his god are actually behind everything, and even using Xykon to their ends.
An even further baiting: The Order of the Stick author Rich Burlew has occasionally written little essays on how D&D is played and storylines are formed on his website. In particular he talks about things like how evil people can have friends, Even Evil Has Loved Ones, and two villains working together aren't always just looking to turn on each other at the first opportunity. Combine that with scenes of Xykon and Redcloak joking together, snarking each other, and commiserating when their cause seemed to be lost, and it seemed like might be such friends. Then StartofDarkness came out and kicked that theory right in the nuts. Well played, Mr. Burlew, well played.
When General Tarquin was introduced he got a lot of fans for affability, savvy, and style. And of course he's Elan's father. It's since become apparent that he uses his position as de facto ruler of the Empire of Blood to force any woman he takes a fancy to to marry him, then kills them when he gets tired of them. Which makes him rather less likable. Not to mention burning 30 slaves (possibly alive) to spell Elan's name out in lights - even Elan finally realizes it at that point.
The same goes for his partner Minister Malack. He's polite, efficient, eschews Tarquin's theatrics, and one of the first things we learn about him is that he hates Nale for murdering his children. Then we learn those weren't his biological children. He's a vampire. One who's planning to outlive the rest of team Tarquin, inherit a unified continent and offer his god a thousand sacrifices a day. "I'm thinking of developing some sort of special chamber by then to make the process more efficient..."
Gunnerkrigg Court has a somewhat literal example with Coyote. At first he comes across as a friendly, Crazy Awesome, and hilarious Trickster, especially when compared to his Dragon, Ysengrin, who seems Axe Crazy. However, as time goes on, more and more hints are dropped that Coyote is really a wild, unpredictable entity that only does things for his own enjoyment, regardless of who might get hurt in the process. His dog kicking has included treating the loyalYsengrin like garbage, threatening to blow Annie’s hand off if she tells anyone about the sword he gave her, and knowingly allowing Reynardine to walk into a trap set by the Court because he thought it’d be amusing. He finally seems to have crossed the Moral Event Horizon after The Reveal that he’s been forcibly removing Ysengrin’s memories and eating them. This is complete with a visibly horrified Ysengrin begging Coyote to stop as the god reaches into his head while sporting a Slasher Smile. This has been lampshaded by Word of God.
In The Movie of Ed Edd N Eddy this is mildly applied. Eddy's Brother is initially portrayed upon his introduction as cool older brother willing to help out Eddy and his friends. It almost seems heartwarming the way Eddy hugs his brother for promising to help them out. One minute later he's beating the hell out of his little brother, his brother's best friend, and has the rest of the cast watching in horror..
In Gargoyles, Xanatos seems honestly remorseful for what happened to Derek, and is trying to make a cure. Then comes the ending, and it's revealed that he has no cure, he just wants to keep Derek close by for further testing and doesn't care at all what he did to him. If there was ever a moment you truly hated Xanatos on the cartoon, chances are this was it.
Directly inverted by Razer in the third episode of Green Lantern: The Animated Series. When Aya frees him from the prison and tells him Hal and Kilowog came to rescue him and need his help, he runs off to their abandoned ship, supposedly leaving them to die. He was going back for his ring, and saves them.
In Ultimate Spider-Man, the Green Goblin finally tells his son the words that his son always wanted to hear: he's proud of him. Then he drops his son to his possible death right after.