Being a sadistic, hypocritical jerk with zero remorse, Dimitri Rascalov from Grand Theft Auto IV is perhaps one of the best examples of a true sociopath played completely straight in the game. This quote by Niko Bellic (in the Deal Ending) puts him best:
"You're a strange man. You killed your best friend. You betrayed everyone who ever came in contact with you. You killed my cousin. I guess...the survival of the fittest thing really meant a lot to you."
A friendly nerdy character in Bully flat out calls Gary, your supposed "ally" in the game, a sociopath, to which the main character doesn't know what that means. It turns out the nerd was right, and all it took was for Gary to run out of medication to become a sadistic sociopathic lunatic who takes control of the entire school, ties up the headmaster, and then attempts to take over the entire town.
Morinth in Mass Effect 2. The mission overview after Samara's loyalty mission even says that her biotic powers would make her an excellent addition to the squad...if her "sociopathic tendencies were mitigated." Though you can kill Samara and recruit her anyway. The codex claims that this is typical of Ardat-Yakshi, or at least much more common than in other asari. How much of this is true, how much is propaganda to justify locking away all Ardat-Yakshi, or how much is just the murderous ones making the rest look bad is left deliberately ambiguous.
Quarian Admiral Daro'Xen displays several classic signs of sociopathy as well. She especially shows it in matters related to the geth, whom she plans to, as a race, mind-wipe and return to their "rightful place" as the quarians' slaves. Tali'Zorah flat-out calls Xen insane when this bit of info comes out, showing that even among the anti-geth quarians Xen's stance is seen as radical. Also, Xen apparently used to perform surgery on childhood toys; Tali's response is predictable. Lastly, she shows unhealthy interest in Legion (your geth squadmate), once expressing the desire to dissect the poor thing to see what makes it tick (which Paragon!Shepard is having none of, by the way).
Dr Henry Lawson definitely counts. He's a Mad Scientist who views everyone as pawns or test subjects for him to use and throw away. Controlled every aspect of his two daughters right down to their DNA and has no problem killing them or using them as Human Shields. He has in fact killed several daughters before Miranda because they weren't "perfect". He also sets up a refugee camp for people fleeing the Reapers, only for them to end up as guinea pigs for his experiments on Reaper tech, by turning them into husks, and killing them when they don't meet his expectations. He claims to be saving humanity, but he's really doing it for his own ego thinking that people in the future would see him as humanity's savior.
Persona 3: Takaya Sakaki hits every qualification for this trope. He's manipulative and a liar; he has a shallow, self-indulgent personality; murders people for fun and money; and most importantly, he absolutely lacks empathy. He tries to kill Ken after trying to goad him to get his revenge on Shinjiro, saying that Shinjiro's words about how such an act would corrupt the young boy have no meaning. He is then unable to understand why Shinjiro would then sacrifice himself for him, a sentiment that he later repeated when one of his fellow teammates sacrifices herself for her love interest.
Tohru Adachi in Persona 4, who initially hides behind the mask of a Nice Guy, though when revealed shows himself as a sadistic manchild who finds entertainment in ruining the lives of others with a tendency of violently lashing out at women who spurn his advances. They do seem a bit more humane in the spinoffs though.
Much like the above, Goro Akechi in Persona 5. He pretends to be a Great Detective who solved many cases (which he himself set up), and, using that persona, infiltrates the Phantom Thieves to lure them to their downfall. Goro ultimately plans on enabling the head of The Conspiracy, to whom Goro is an illegitimate son, to achieve his goals, but then betraying him to bring about the end of his political career and force him to spend time with his son, without caring about all the death and suffering this would cause.
Vanitas seems to fit the mold at first, but the origins of the Unversed prove he is a subversion. Rather than being callous and lacking in anything but the most shallow emotions, Vanitas is comprised of nothing but negative emotions. And he creates a new Unversed with every negative emotion he has. A true sociopath would not be able to feel deeply enough to create them in the first place.
Nobodies are by their very nature sociopaths, since they lack the hearts required to form bonds or experience true emotions. The members of Organization XIII function at varying levels, with the exceptions of Roxas and Xion, the former of which is born under very special circumstances and the latter of which isn't even a Nobody. Another member, Axel, does gain emotional care for Roxas and Xion after hanging out with them, but it's only for them; he is still a sociopath in regards to anyone else.
And then Dream Drop Distance reveals that all the nobodies had the potential to grow new hearts and feel emotions all along. Bringing this trope Up to Eleven with Xemnas, the one who lied to them and made them believe they were Sociopaths all in order to manipulate them and gain control of their minds, hearts and bodies. And though he acts the most emotionless of them all, he likely had Terra's heart all along meaning he was just naturally an uncaring monster.
Played absolutely straight with Master Xehanort, the Big Bad of the series and a human to boot, who fits all of the criteria.
Irenicus and Bodhi from Baldur's Gate II: Shadows of Amn. In their case, it's a magically caused condition, though from what we hear, they weren't exactly nice people before.
The real Alex Mercer from [PROTOTYPE]. After all, he "wasn't paid to feel." He was so bad that even The Virus who has taken over his body is a better person than Dr. Alexander J. Mercer ever was.
Relius Clover, An unabashed Mad Scientist and Abusive Parent extraordinare who, after gaining the ability to see a person's inner soul, views other human beings as tools to be manipulated or guinea pigs to be experimented on. And in what can only be considered a seriously messed up logical extreme of the page quote, he even turned both his daughter and his wife into puppets! Completely unapologetically. For Science! And then he attempted to kill his son when he demanded an explanation.
Izanami is a classic Sociopath. She is charismatic, manipulative, and wickedly intelligent, even through her batshit insanity, but is simultaneously utterly bloodthirsty and utterly devoid of anything remotely resembling empathy.
Danny St. John from The Walking Dead, while Danny himself is mostly not explored, due to his limited amount of time on the game, we did find out, he was a cannibal, he killed Jolene just because she knew his secret, and he even gave Lee tips on how to cook him when he got trapped in the beartrap.
From Season 2, we have one William "Bill" Carver, who is happy to beat a man almost to death, smack around an eleven-year old girl, and candidly and remorselessly admits to killing Reggie in cold blood if Bonnie asks. More worrisome is that he says he claims Clementine is Not So Different, although how the truthfulness of this statement is up to the player.
Dahlia Hawthorne from Phoenix Wright: Trials & Tribulations. She is arguably the cruelest and most evil character in the entire series, and has the longest list of intended murder victims out of any of the other killers Phoenix has encountered. At one point, she explicitly states that she has never cared for anyone or anything aside from herself, and she plots to kill Maya simply to get back at Mia from beyond the grave.
Also, Matt Engarde from the second game. He's so disconnected from any sort of moral compass that he honestly believes that he's innocent of murder because he didn't kill the victim himself, despite hiring the assassin who did.
Dual Destinies gives us the rather creepy example of the Phantom (AKA Imposter Bobby Fulbright). According to a psychological profile done by analyzing his vocal inflections, he experiences little to no emotions. However, as his disguise proves, he's very good at faking them. He gives the perfect performance of appearing happy when Blackquill says he believes in Imposter!Fulbright's innocence, only for Athena to reveal that there's no indications of the actual emotion of happiness in his voice. When she tries to put his testimony through the Mood Matrix, he first comes up as completely blank. When he's called out on this, he then makes his emotions fluctuate so much that it's impossible to get a reading on him. Exactly how this works is left unexplained, but he implies that he simply trained himself to not feel emotions, hence his ability to fake them. Although it turns out that whether or not he'll admit it, he does still feel one emotion - fear, as brought on by the threat of death.
Likewise, Calisto Yew from Investigations. For most of the case, she's simply a Jerk Ass defense attorney who is using her corporate clients to investigate the smuggling ring that killed her sister Cece Yew. Except that Cece Yew had no sister. Calisto was sent by the smugglers to pose as her in order to trip up Prosecutor Faraday and Detective Badd's efforts to bring them down, becoming The Mole of their three-person Yatagerasu and playing the part perfectly for several years. When part of her identity is uncovered she describes how she loved the thrill of breaking into her client's offices to steal their secrets and says that Edgeworth's investigation is giving her the same thrill. She also murdered Faraday without hesitation or remorse, did a very good job at disguising the crime scene, and didn't bat an eye that Faraday's kid was in the courthouse that day—then she nearly murders Edgeworth before escaping and becoming Shih-na to hamper Shi Long Lang. When she's eventually exposed, again by Edgeworth, she betrays her boss by dropping incriminating evidence. The only genuine emotions she ever shows are either amusement and mockery, or excitement over a battle of wits and has no remorse for betraying everyone she ever works with.
Manfred von Karma is an arguable case. On one hand, he is shown to only care about his perfect trial record, completely willing to ignore the fact that he could be condemning any number of innocent people to prison. He also considers Gregory Edgeworth getting him a penalty and ruining said perfect record to be sufficient grounds for murdering the guy and raising his son to believe he did it and grow up to be the sort of person Gregory hated.Miles Edgeworth: Investigations does have a flashback case that implies that von Karma really did care for Franziska and Edgeworth, however the fact that he pretended to want the best for Edgeworth while very clearly intending to frame him for murder all along throws into question if he really felt that way or was just faking.
Blaise Debeste is even worse than Manfred. Outwardly as childish and playful as Dahlia is innocent and sweet, this person is cold, cruel, calculating, and heartless, seeking only to further their career. He mistreats his own son, belittling him so much that even the usually icy Franziska feels sorry for him and actually offers him a bit of advice, due to her own experience with a corrupt prosecutor for a father. At one point, Debeste even aids in a presidential assassination, alongside the equally black-hearted Patricia Roland. Incidentally, this person is responsible for actually giving Manfred the penalty on his record that caused the DL-6. And he's the one who GAVE Manfred the false evidence that caused the mark on his record in the first place.
Ga'ran from Spirit of Justice is another big example. She's more than willing to use her authority as queen to have hundreds of people executed, thinks nothing about using her sister's family as pawns that she uses as blackmail material against each other, and thinks nothing of directly murdering anyone who would prove disadvantageous to her, and was disturbingly okay with letting a baby die in a fire. And to top it all off, she has a grandiose sense of entitlement, going as far as to rewrite the law itself in the middle of court to make standing up to her a crime punishable by immediate execution. She is never shown to care about anyone other than herself, and is an abusive foster mother who is more than happy to belittle and insult her own foster daughter/niece Rayfa at every turn.
Really, a good deal of Ace Attorney's multiple-murder killers are either outright sociopathic or borderline.
Hades from Kid Icarus: Uprising. He instigates a pointless, international war that results in the deaths of millions of humans for no other reason than to harvest their souls to either create more underworld monsters and do whatever else he wants with them (As well as for his own sick amusement), and has absolutely no remorse for his actions. Even when he helps out during the Aurum Arc, it's not out of alturism, it's only because he wants to be the one to destroy humanity. and he still throws Underworld Monsters in Pit's path to hinder his progress just to screw with him.
Luca Blight from Suikoden II, the "MadPrince" of the Highland kingdom. You get a good idea of his personality in his Establishing Character Moment in which he orchestrates a massacre of children training to be soldiers on his side to rally up support to restart a pointless war with a neighboring nation, while mocking their deaths and regretting not joining in the massacre. He continues to commit atrocities throughout the game, brutally killing scores of people For the Evulz including his own father, while displaying a level of sadism and Lack of Empathy that disturbs even his underlings. Even during his Final Speech, he not only displays a complete lack of regret for his horrific actions, but actually boasts triumphantly of them while reveling in his unredeemably vile nature.
Colonel Jade Curtiss from Tales of the Abyss is a high-functioning example, and very much aware of it. Formerly a Child ProdigyBlack Mage who tortured monsters for fun, he could have been much worse if a mentor hadn't stepped in to give him some sense of morality. As is, his old mistakes haunt him, and it troubles him somewhat that he doesn't understand what it means to end a life.
Rommy in Tales of the Tempest. She has no regard for morality or empathy, and does things (usually manipulating others and killing people) only because they amuse her.
Syndicate (2012): Agent Merit's dossier remarks that all Agents are expected to be psychopaths, but Merit is psychopathic even by Agent standards. Also, the corporate, ethically bankrupt Syndicate society effectively fosters a general attitude that the lives of others are meaningless except to the extent they can be used to benefit yourself.
Super Paper Mario gives us Dimentio who is for all intents and purposes, Mario's Kefka Palazzo and one of the most disturbing examples of this trope in a Mario game. Hiding his monstrous intentions under the veneer of the ditzy jester, he uses his superficial charm to manipulate everyone in the game in order to obtain the Chaos Heart and remake the multiverse in his own image. And it's implied that he's motivated solely by his insanity. He's also very sadistic, killing Mario and the gang with no remorse and cracking jokes about their deaths. He also views love and similar emotions as weaknesses to be exploited. His last act, however, is what hammers home his sociopathy. When defeated for the final time, he leaves a shadow of his power behind to continue controlling the Chaos Heart to ensure that everyone in existence will die with him. Meaning his last act was one that would ensure the deaths of untold trillions. There's a reason why he's considered one of the darkest villains in the Mario series.
Mario & Luigi: Partners in Time has Princess Shroob, the leader of the Shroob race. Though she has the sympathetic motive of finding a new home for her Dying Race, this motive falls horribly flat as she commits various actions that seem driven by pure sadism. Two notable examples are feeding Princess Peach to Petey Piranha in front of a Shroob audience and shooting down the Koopa Cruiser while laughing. Her Lack of Empathy also seems to extend to her sister as she made virtually no effort to free her from the Cobalt Star and showed no indication that she intended to.
While most of the villains in Eternal Sonata are bonafide psychopaths, the two who stand out the most are Fugue and Waltz. Fugue is the sadistic Evil Genius of the group who's Establishing Character Moment has him attacking Frederic and Polka just because he's wet. Waltz is just as bad, if not worse. He creates a substance called mineral powder which is said to cure diseases, but also has a side effect of turning people into monsters. Why does he want to do this? So he can have an army to help rule the world as he feels that this is the best way for people to remember him.
Kyrie Ushiromiya in Umineko: When They Cry displays quite a few elements of this. While she appears to be nice and smart, she also always shows a cold, calculating side, keeping either a faint smile or a deadpan expression. There are a few red flags of her sociopathy in Episode 3 and 5 (where it's mentioned that she can sometimes "think in an extremely cold and ruthless manner"), and Episode 7's Tea Party makes a full display of it. Not only does she claim that she doesn't give a crap for her daughter Ange, but she isn't overly shaken by the death of her husband and accomplice either, and is in fact rather pleased that he is out of the way. Add to that a brief Hannibal Lecture to Eva, and you have one of the scariest characters of the series.
Possibly Kotomine Kirei of Fate/stay night. He describes himself as never feeling happiness from the happiness of others, only finding joy in their pain and suffering, and being incapable of loving someone else. Interestingly, because he was born to a very religious man, he considers himself a "defective person" and spent most of his life trying to "fix" himself, only to give up ten years before the story. His ultimate goal is to try to understand why a good and loving God would create a seemingly inherently evil person such as himself. He is definitely cunning and manipulative, an excellent liar when he wants to be (he prefers to amuse himself with Brutal Honesty), and is charming in his own way, although the story's protagonist takes an instant dislike to him. Said protagonist later realizes that he actually does like Kotomine, and that the reason he immediately felt a twinge of distaste was because he realized that he subconsciously saw a BIT too much of himself in Kotomine.
Seth, the CEO of S.I.N., is an Evilutionary Biologist who views others as nothing but test subjects and will freely manipulate others to get what he wants. He hosted a tournament to lure Ryu and use his his Satsui no Hadou to complete his BLECE project. Much like Bison, he is extremely arrogant and seeks to rule the world and prove his superiority over humans.
Injustice: Gods Among Us has The Joker, as usual. Or rather, his Injustice counterpart. The Joker in the game proper is more of a Nominal Hero and doesn't get much screen time. But his Injustice counterpart take the sociopath trope Up to Eleven. He is the direct cause for all of the misery that happens in the game. Five years prior to the game, he planted a trigger for a nuclear bomb placed in the heart of Metropolis in a pregnant Lois Lane designed to go off the instant her heart stops beating. He also drugged Superman with Krytonite-laced fear toxin, causing him to see Lois as Doomsday and kill her by dragging her into space so that the deaths of Lois, his unborn child, and all of Metropolis were on his hands. And the reason behind this horrific act? He was tired of his constant defeats to Batman and wanted an easier opponent.While the Joker ultimately pays for it with his life, his actions caused Superman to develop a zero-tolerance policy towards crime and ultimately turns the Man of Steel into an even worse monster than he was. The fact that the Joker gives one final laugh as he dies shows he was fully aware of this fact.
Clockwerk of the Thevievus Raccoonus. A psychopathic owl and rival to Sly's family that was driven solely by his hatred for them. To that end, he turned himself into a Cyborg just so he could achieve Immortality for the express purpose of hunting down and killing each of Sly's ancestors, ending with his father. Clockwerk's Lack of Empathy is so great that he's not only incapable of feeling empathy, but he also views it as a weakness in others.
Neyla of Band Of Thieves. At the outset of the game she was depicted as a Interpol cop with Black and Grey Morality who assists Sly and his gang, but after Ch.3 she reveals a glimpse of her true colors when she betrays the gang and has them arrested, even framing Carmelita as well. Her true colors are fully exposed during the finale where she is revealed to be working for Arpeggio, the leader of the Klaww Gang, during which she betrays him and steals the Clockwerk body for herself. Her repsonse to Arpeggio's astonisment at her betrayal showcases her Lack of Empathy.
Neyla:Stupid Arpeggio. I double crossed Interpol, The Cooper Gang, and The Klaww Gang, What made You think I wouldn't do the the same to you?
Arcturus Mengsk from StarCraft. Reviewing his key personality traits is like reading through a sociopath diagnostic checklist: superficial charm, a grandiose sense of self, pathological lying, a penchant for manipulating others to achieve his own ends, an absolutely astonishing lack of empathy or remorse for any of his actions, and an insatiable lust for power and dominance that drives his every move. He unleashed the Zerg on a planet populated by billions of people just to overthrow a few hundred individuals at most and establish himself as the preeminent political figure among the Terrans of the Koprulu sector. He has no qualms whatsoever about sacrificing those closest to him if it suits his purposes.
The Legend of Zelda series has pulled out its share of notable sociopaths over the years. In order of appearance.
While it's mostly a case of Depending on the Writer, most incarnations of Ganondorf are typically depicted as textbook sociopaths. A power-mad despot feels no remorse for anything and will stop at nothing to obtain the Triforce and rule Hyrule even if it means using murder and manipulation. The only exception to this rule is his Wind Waker incarnation, who was portrayed as a Tragic Villain and a Well-Intentioned Extremist.
Majora's Mask is a textbook example. It loves all of the pain and destruction it causes, cares nothing about the consequences of its actions, and sees everyone else as nothing more than puppets and playthings to use and throw away.
Twilight Princess has Zant. He was a member of the Twili race who went insane when denied the title of king for his ambition to conquer the World of Light. After making a deal with an imprisoned Ganondorf for power, he seized the throne by force, turning Midna into an imp and transforming his own people into Shadow Beasts by sealing away the Sols. He then led a full fledged invasion of Hyrule, committing more atrocities along the way such as executing Queen Rutela in front of the Zoras for resisting his rule. and forcing Zelda to surrender by threatening her people. When Link and Midna unravel his plans he curses Link to remain in wolf form permanently and fatally wounds Midna by exposing her to light. All done with no remorse whatsoever. The fact that he has the gall to pass himself off as a well intentionedKnight Templar only reinforces his sociopathy.
Skyward Sword has Ghirahim an arrogant and extremely sadistic Demon Lord who seeks to use Zelda's life force to revive his master Demise and pursues this goal with total disregard for the lives around him. Going through his personality traits is going through a sociopath's checklist: superficial charm, feels no remorse for anything, extremely sadistic and relishes the pain he inflicts on others, and will not hesitate to manipulate others if it serves his ends.
A Link Between Worlds has Yuga. A vain and arrogant sorcerer who at first glance seems to be a mere servant of Hilda, helping her in her quest to use Hyrule's Triforce to restore the kingdom of Lorule. At the end of the game, he reveals his true colors when he reveals that he never cared about Lorule's fate and that he was merely using her to obtain all three pieces of the Triforce and rule Lorule as the god he fancies himself as.
A sub-race of this trope is created in the latter parts of the Mega Man X series in the form of the "New Generation Reploids", Reploids with a copy chip installed which allows them to take the form of any Reploid whose artificial DNA Data is included in the chip (and which can add more Reploids not initially included on the chip by somehow extracting the data from them during battles). The trouble is, the DNA Data of Sigma, which has fundamentally merged by now with the MaverickVirus itself, was included in all the chips save for that of a prototype called Axl. This allowed the "New Gen" Reploids to voluntarily "infect" themselves, essentially turning off their consciences at will, by accepting Sigma's twisted evolution philosophy as their core interpretation of right and wrong. Very quickly this culminated in two new Maverick outbreaks, from Mega Man X8 and Mega Man X: Command Mission, both turning out to be the results of conspiracies spearheaded by a "New Gen" Reploid looking to take over the world.
The Mega Man Zero series has Dr. Weil, who is one of the few villains in the franchise that could qualify. Everyone's a disposable pawn to him, and he refuses to let anything that he can't control exist.
Doctor Eggman in Sonic the Hedgehog is a family-friendly version. Firstly, he has no conscience to speak of, using living creatures as batteries and by extension, experimentation on sentient beings. He is determined to take over the world purely because he deserves to rule the world - while at the same time not being exactly clear on what he'd do afterwards. As well as this, he is always prepared to briefly ally with Sonic against greater evils, then toss him aside once he has no use. He has been known to lie without the twitch of a mustache. Most obvious is his vanity - despite his many, many failures, he continues to fight Sonic with very little variation to his methods. Continuing in that vein, he is portrayed as also being charming and polite even to his enemies. Like most real-life Sociopaths, he also lacks Character Development - while his origins have expanded over the franchise, his goals and methods remain the same.
The only version of him that ISN'T a sociopath is the Dr. Robotnik from The Adventures of Sonic the Hedgehog, and that's mostly due to being a comedy villain antagonist that is a Jerkass instead of a sociopath. Contrast with the SatAm version, who not only plays being a sociopath straight, but lacks ANY of the comedic attributes that his other incarnations have while being the only version of Dr. Eggman that actually SUCCEEDED in taking over the world as part of the show's backstory.
Ellen of The Witch's House is a textbook example. She cares only for herself, acts as a False Friend to the kind Viola, betrays her "friend" when she's no longer useful to her, is an Ungrateful Bitch (feeding a frog to a giant snake after it had done nothing but help her, and betraying Viola despite all she had done for her), has no empathy and is a total sadist (taunting Viola about her fate and snickering after she is killed by her own father), and naturally, she is not redeemed. However, usually for a sociopath to the point she may be a subversion, everything she does is motivated by her desire to be loved by both parents and friends. When she could receive neither, she turned to magic and began killing, and it's shown in her backstory that many of her first kills (her parents, a boy who ran away after seeing her true form) were only made after she thought they showed no love for her. The reason she was so dead-set on stealing Viola's body in the first place, aside from getting one that didn't hurt, was because she knew Viola had a kind and loving father, something she never had, and she wanted him for herself. Of course, that's assuming she didn't eventually start seeing "love" as a possession to be hoarded.
In Planescape: Torment, The Nameless One's "Practical Incarnation" was this. Ruthless and completely willing to destroy lives to fulfill his goals, he was responsible for many awful things you learn of through the backstory, including your party's Dysfunction Junction status. Notably this is why he's called Practical rather than Evil like one would usually expect; he did evil things not out of enjoyment of them, but simply because he was convinced they were the most effective and practical ways to get what he wanted.
Not Important from Hatred is given little backstory, but states that his "whole life is nothing but cold, bitter hatred" immediately prior to loading up several automatic weapons and going on a massive killing spree, showing little emotion as he does so.
A subtle version of this occurs in the Fallout: New Vegas DLC Lonesome Road. Should the player progress through the area with a positive reputation with any of the three dominant factions in the Mojave, Ulysses will accuse them of being an unthinking pawn of a larger, flawed organization. If the Courier has a poor reputation with all three factions Ulysses will accuse them of being a selfish, shortsighted malcontent who blunders into circumstances with far-reaching implications without the slightest concern for how their actions affect others.
Flowey from Undertale is a huge one. He cares about no one but himself, exemplified by his philosophy of "kill or be killed." His monologue in the Genocide run reflects a more sympathetic portrayal of The Sociopath than most. Flowey is legitimately upset at his Lack of Empathy, but years of living without the capacity for love have driven him to his sociopathic nature by the beginning of the game, doing whatever he can to feel it again.
Justine from the Amnesia: The Dark Descent expansion pack of the same name is strongly implied to be one, with a healthy dose of Narcissistic Personality Disorder on top of it. She captures her three suitors, tortures and mutilates them to roam her dungeon along with several other hapless bystanders who get roped into a sick "game" of hers where she forces a young woman actually Justine herself after taking a Laser-Guided Amnesia potion into Sadistic Choices about whether or not to save them or be killed herself. Also of note is that Justine's father was a psychiatrist and clearly knew something was wrong with her (and the game is set prior to sociopathy being fully defined) before she killed him.
Ruvik from The Evil Within. Showed sociopathic tendencies at first by dissecting animals, and when Laura was assumed to have died, moving on to people. His response to Dr. Jimenez's horror about the victims of his traps seals the deal on this one:
Ruvik: "These vermin? These microbes? They're mine to deal with as I please."
Zero Time Dilemma has Mira, who, despite seeming normal, is in fact entirely unable to understand emotions, something which drove her to becoming a brutal Serial Killer who cuts out people's hearts in an attempt to comprehend their feelings. She also doesn't care at all for her boyfriend Eric and plans to kill him too. In the epilogue files, though, it turned out that Eric convinced her to turn herself in, and she was honestly pondering how she could redeem herself.