In And Then There Were None, Anthony Marston has zero remorse about running over and killing two children with his car and doesn't even seem to comprehend that the children's deaths may be more serious than the loss of his driving license. The Poetic Serial Killer selects him as their first victim because his complete lack of empathy meant that he was literally incapable of realizing that what he did was wrong and wouldn't experience the psychological torment and guilt the killer wanted their later victims to suffer through.
A Brother's Price has Keifer Porter. Very vain, charming if he wanted to be, good at manipulating people, even though he was rather stupid otherwise, and ready to do horrible things with little or no provocation. He is also implied to have been easily bored. While he did sleep with his sister, he seems to have been unable to form emotional relationships, seeing as his wives adored him and did everything to keep him happy, which didn't stop him from torturing their little sister. And killing her father, and taking part in a conspiracy to kill them.
Kazou Kiriyama from Battle Royale has no qualms about letting a simple coin toss decide whether he'll play the game to win or try to fight it, killing multiple classmates of his in very painful ways and even seems impervious to a lot of pain that would cripple other people. He even cut his own arm open and taped a tendon differently so he'd regain usage of his index finger. It's revealed that his behavior likely came from a birth defect.
The movie version depicts him as more of a sadist, having volunteered for the program, relishing every moment of his violence. One moment in particular has him gunning down two people trying to call for a truce, broadcasting their screams of pain through a megaphone.
Mitsuko Souma is equally ruthless and seemingly remorseless as Kiriyama when it comes to killing her classmates, although she turns out to have one hell of a Freudian Excuse, as it's later revealed that she has, among other things, been raped and sexually abused multiple times since the age of nine. As a result, she feels dead inside and doesn't care about anything but protecting herself.
Kawada even compares the two, and correctly identifies that while Kiriyama was likely born an Empty Shell, Mitsuko's cold-blooded nature likely developed as a response to her Dark and Troubled Past.
Kevin Khatchadourian, the eponymous character of We Need to Talk About Kevin. A teenage school shooter and torturer, he has been a monster ever since he was a young child. Kevin has a severe case of APD/sociopathy; his disorder results in him never relating to other people and finding everything to be dreary, pointless and uninteresting. Every day of his life. By the time he is a teenager, he exists in a constant state of And I Must Scream.
Discworld has Jonathan Teatime in Hogfather. According to the book, he "sees things differently from other people, in that he sees other people as things." He even spent a significant amount of his time theorizing how to kill the various holiday entities of the Disc, like the Hogfather, the Soul Cake Duck, and DEATH himself.
Lady Lillith has shades of this as well, what with being a high-caliber Tautological Templar. While not quite as Ax-Crazy as Teatime, she's likely done at least as much harm in the long run, most of it presumably more long-lasting. Never once does she stop to think if her idea of "good" has anything in common with other people's.
Lord Voldemort is a textbook sociopath. In his younger days before he became Obviously Evil, he was a canny manipulator brimming with superficial charm. He does not understand love, viewing other people - including his own followers - as merely tools to serve his ends. Also, the "persistent killing" part fits him pretty well.Though the book posits a reason for his sociopathy. His mother seduced a Muggle with a love potion, and it was a completely loveless union. Riddle Sr. did not truly love Merope back, displaying affection only under the influence of the potion. This absence of love in Voldemort's conception was the reason for his complete inability to love. Dumbledore also believes that had his mother not lost the will to live and died in childbirth, but instead raised Voldemort and loved him, his sociopathic tendencies might have been avoided.
Delores Umbridge enforces the law as she understands it, takes any opportunity to dominate those under her station or rid herself of perceived opposition, lacks any sense of morality (especially towards people with non-human bloodlines like Hagrid or Remus Lupin, and in the final book even Muggleborn witches and wizards), uses likeminded people for her own ends, and sees everyone as expendable in service towards her goals.
Bellatrix Lestrange and Barty Crouch Jr aren't far behind Voldemort. Both are unrepentant serial killers and torture tacticians, fanatical racists, mentally unhinged, both having murdered family members of their own (Bella killed her cousin Sirius, while Barty killed his father Barty Crouch Sr) utterly devoted to Voldemort who they seem to revere as a deity and may be their only true "attachment." Case in point, Bellatrix is married but does EVERYTHING she does for Voldemort, whom she is said to "love." Barty on the other hand, is not stated to have loved either of his parents, completely disregards the fact that his mother sacrificed herself to get him out of prison and immediately sought to rejoin Voldemort. Upon re-entering the services of Voldemort, he begins torturing, manipulating and killing again. It can even be construed that his tears during his trial were a farce in an attempt to manipulate his dad to not throw him in jail.
Though many of the supernatural creatures in The Dresden Files exhibit elements of sociopathy (notably vampires who fully embrace their predatory nature and many of the nastier Winter Court sidhe), the most obvious example is the all-too-human Nicodemus, a man so thoroughly and unapologetically (and yet often politely) evil that a Fallen Angel works with him as a genuine partner. In Skin Game he even refers to himself as a sociopath (correcting Dresden, who called him a psychopath). Nick's wife Tessa and daughter Deirdre are also candidates.
Henry Bowers in IT by Stephen King is a prime example of a sociopath, as he matures from a schoolyard bully to a murderer. Had he not been institutionalized, he likely would have ended up eventually going on a shooting spree.
In the same book, Patrick Hockstetter is explicitly described as a sociopath, with no grasp of the fact that others are, in fact, real, and at five years old killed his baby brother for disrupting household routine. IT even has trouble finding a humanoid form that Patrick will comprehend and become frightened of, briefly turning into a writhing, amorphous blob.
In the gruesome flashback scenes in the Inspector Lynley novel This Body of Death, one of the three boys shows most of the listed traits. As an adult and one of the murder suspects, he turns out to be innocent and eventually dies redeeming himself. Since the author has a degree in psychology, this may well be intentional.
Count Olaf of A Series of Unfortunate Events. He burns down a hospital to cover his tracks, kills at least one person per book to further his agenda, seems to view violence as rather entertaining, is extremely narcissistic, has a sense of entitlement to a fortune that isn't his and is able to manipulate and charm anyone but the children. Oh, and he's perfectly willing to kill children.
Subverted in book 13 when we find out he loved Kit Snicket and he saves her life and is shocked that the Baudelaires would even think that he would hurt their parents. Also, he has a Freudian excuse - it's implied that the Baudelaire parents killed his parents with poison darts.
IvarRagnarson of The Last Light of the Sun. He doesn't see people as people, murdered his sister for laughing at him, sheds no tears over his dead brother, has to keep reminding himself to speak to people as though they were equals, and loses his temper when irritated. At one point he murders a captured earl just to make sure the mercenaries he's hired won't think of just ransoming him and going home; Ivar has lots more For the Evulz murder and mayhem planned for them. He's the bad guy.
Caine from Gone is confirmed by Word of God to be a sociopath. His Lack of Empathy becomes clear early on, but his status as this is confirmed when he tells a pack of mutated coyotes that they can feed on young (some daycare-age) children because . . . there was no reason not to. He actually manages to be a nuanced character, though; the real monster is The Dragon, Drake.
The movie's central plot essentially is the interplay of two sociopaths. Dickie Greenleaf (Jude Law) is a rich kid who's bumming around Europe on his plutocrat father's dime. Tom Ripley is a young blue collar musician willing to impersonate a fellow Princeton grad, defraud Dickie's father of a rather nice expense account to "convince" Dickie to come back, then play Dickie off his father to bum around Europe. Both display a great deal of superficial charm, little remorse about lying and manipulating others, quick tempers, a willingness to lash out violently when it suits them, and no qualms with defrauding the old man. Dickie has no problem blowing off a young Italian girl he impregnated, and when she is Driven to Suicide, he seems more upset at how this affects him. Tom lies his way into high society and is willing to lie, steal, and murder to stay there. Marge, Dickie's girlfriend, describes how when Dickie takes note of you it's like being in the sun. This is a common trait among sociopaths. Tom has a similar trait and facility for lying. The few moments where either shows an emotion similar to remorse may seem to break the mold, but even real sociopaths are not completely inhuman. Sociopathy exists on a sliding scale.
In the RCN series, Adele Mundy's assistant/bodyguard Tovera is a complete sociopathic monster who knows she needs Adele to act as her conscience to keep her functioning in society, and enjoys, as much as she can be said to, serving Adele (and by extension, Daniel Leary) because it gives her plenty of opportunity for authorized mayhem. For her part, Adele is very scrupulous in not asking Tovera what she does in her free time for amusement when she disappears into the city's slums.
JohnWayneCleaver is a deconstruction of a sociopath: he's completely aware that he is nothing less than a nascent serial killer who has yet to kill anyone, but is also every bit as aware that acting out his fantasies of killing would ultimately lead to his arrest and execution. Having to kill someone to save his mother's life at the end of the first book seriously fucks him up, and leads into the plots of the other two.
In the Red Dwarf novel "Last Human", the alternate Lister is a full-fledged sociopath, nicely outlined in his psych profile.
RichardLopez of Ship Breaker is a drug-addicted, Axe-Crazy, Archnemesis Dad who suffers from massive mood swings and a severe inability to connect to other people. He has no qualms about threatening to maim his son, or cut out a girl's eyes, and eventually tries to sell Nita's organs on the black market. His attitude towards his son, Nailer, is especially volatile, shifting from almost fatherly affection to an attempt at Offing the Offspring at the drop of a pin. He kills without remorse, and no one, not even Nailer, is sad when he dies.
In the Privilege series, Kaitlynn Nottingham is this. She kills her best friend's dad, who happens to be her lover, and has no qualms with killing one of her classmates so she can get into a secret society.
John Dread of Otherland is explicitly described as a sociopath, complete with a psychologist telling the police how he was the scariest person he'd ever attempted to treat, because he could tell that Dread did not see him as a person, but merely an object, to be evaluated on his usefulness and killed without a second thought if he became too inconvenient. Dread is given the Freudian Excuse of a drug-addled prostitute mother who brutally abused him in order to turn him into a weapon against the world she hated. It worked.
Sick Boy is a borderline example. He exhibits all the traits of a sociopath, such as a distinct Lack of Empathy, a highly manipulative streak, a grandiose sense of self worth, and is superficially charming. However, there are a few instances that suggest otherwise. Ultimately, it is left up to the reader to come to their own conclusions.
Alan Venters is a pretty clear cut example. A rapist and wife beater who knowingly infects someone with HIV and shows no remorse for his actions, his only redeeming quality is that he genuinely loves his son.
Jadis the White Witch from The Chronicles of Narnia is up there with Iago. Superficial charm? Check. Above average intelligence? Check. Pathological egocentricity? You betcha! Incapacity for empathy or remorse? "So much for love."
In the Young Adult novel Rosebush, it turns out that Langley Winterman is this, as she's the mastermind behind the hit-and-run and she casaully uses and manipulates people to get what she wants.
The eponymous character from the novel Elmer Gantry. Elmer is a charming, jocular preacher who is motivated entired by self-interests and appetites. He has no moral qualms about lying, marital rape, or moral hypocrisy. The film version depicted Elmer more as a loveable scamp than an outright sociopath.
In Across the Universe, Luther is shown to be completely without remorse in any of the stuff he pulls, from trying to rape Amy to raping Vittoria in "revenge" after Amy escapes to trying to incite riots after the population is taken off their mass-spread sedatives to continuing to stalk and harass Amy, wanting to finish what he started. The only reason he seems to have for any of the things he does is that he enjoys having power over others. The only reason he changes his behavior at all is because Amy fights back and makes it clear she'll shoot him if he continues. Even then, he still enjoys scaring her.
While Patch from Hush, Hush is intended to be heroic, he also shows quite a few signs of being sociopathic, particularly in the first book. He frequently engages in dangerous fights and such just to amuse himself and shows little to no remorse over the fact that he stalked Nora and made several attempts on her life. By Nora's own admission, he's disturbingly good at hiding how he feels and manipulating her. He also shows no remorse or regret over enslaving a Nephil for several centuries, essentially condemning the poor guy to an eternity of having his body stolen by Patch for two weeks out of every year, usually for the purpose of sex with unsuspecting women.
Simona Ahrnstedt has Edvard Löwenström in her debut novel Överenskommelser. He was a sadist, who enjoyed hurting women for pleasure. He made a deal with a fellow sadist that he would get his cousin, even though he knew that she would suffer. He made a 14-year-old girl pregnant, but still abandoned her. When she died after an abortion, he felt no remorse. And when his sister was seriously ill, he felt no sadness about it. He practically wished that she would die, so his parents would think about something else other than his atrocities. He made sure that his cousin was separated from her love interest, which gave her no other choice but to get married to the disgusting man, to whom he and his father had promised her. When his cousin was raped and almost killed on her wedding night, his response was that she only had herself to blame! And he also raped at least one woman, even if that was off screen. Edvard never felt any remorse for anything he did, and he was unable to feel love even for his family. Neither could he feel gratitude. He was too easily bored, which actually is another sign of sociopathy.
Roland Birgersson in "Betvingade" seems to fit into this trope as well. He has already murdered a woman and now plans to murder her son (who happens to be Markus Järv, the story's male protagonist) as well. And he's prepared to also murder Markus's wife and/or let Markus's six-year-old daughter drown to get his way. And to make things worse, it also turns out that Roland is Markus's father.
Shelly Longpeire in The Troop displays the classic signs; Lack of Empathy, manipulative streak, tortures small animals to death for fun, etc. He even tricks Ephraim into skinning himself alive.
Nick Dunne in Gone Girl has shades of this, and even admits to some of the traits. His wife Amy, however, wins the Olympic gold medal in sociopathy. She faked her death and framed her husband for murder as revenge for his infidelity and their crumbling marriage, going to absolutely astonishing lengths to pull off the "perfect crime", and it's hardly the first time she's carried out Disproportionate Retribution against somebody who wronged her (or who she merely thought had wronged her), nor is it the last. She checks off nearly every one of the traits: she's a Consummate Liar and a Manipulative Bitch with a distinct Lack of Empathy and an inability to forge personal connections. And she's damn goodat hiding it.
The Revenge of the Sith novelization has Dooku, who checks all of the boxes except for number three: he is incapable of caring about the countless victims of his dreams of empire, he has managed to fool even the Jedi into thinking he's a decent person, he's a tremendously smug asshole when facing Anakin and Obi-Wan, and the closest attachment he develops to anyone is viewing them as an asset rather than a threat.
One Flew Over the Cuckoo's Nest has Nurse Ratched. She seems nice at first, but she is actually a very controlling and manipulative woman. She cares nothing for her patents and wants to remain in control of the hospital. Ironically, in real life, a person like her would be in a mental hospital for treatment.
Hugo Lamb from The Bone Clocks is a textbook example. Outwardly charming, his inner monologue reveals him to be a womanizer, a consummate liar, a thief, and an expert manipulator, who has no qualms about using others for his own ends. Hugo eventually takes a level in evil by joining the Anchorites, an ancient brotherhood who make themselves immortal by destroying other souls.
While the word is never used to describe him in-universe, Erik from Tangerine definitely fits this trope. Arthur Bauer probably counts as well.
Caligula from I, Claudius. The TV adaption plays up his delusions, but the book emphasizes a closer-to-earth depravity.
O'Brien from Nineteen Eighty-Four. He takes the "deceptively charismatic" aspect of the trope so far that Winston finds himself feeling a begrudging admiration for the man even as O'Brien is torturing him. The ultimate goal of the Party is to create a world entirely of sociopaths, where any attachment between individuals will be eliminated and everyone will care for nothing except what benefits the Party.
The villain in Eden Green is infected with an alien needle symbiote that takes over his mind and acts to ensure his (their) survival. When under its influence, he becomes manipulative, immune to guilt, and casually vicious. Later, the title character is infected and begins to succumb to the same effects.
East of Eden: Cathy Ames is a consummate liar and master manipulator, considers herself superior to everyone else, is completely self-centred and has no empathy or shame. In the chapter where she's introduced, the narrator all but mentions the trope by name in describing her, claiming that in the same way some children are born with physical deformities that leave them missing arms or unable to see, Cathy was born with a deformed soul that left her missing a conscience and morals.
Steerpike from Gormenghast is played completely straight with absolutely no effort to humanise him. Peake manages to write the character so well that he becomes strongly likeable to the reader even though they can hear his inner monologue and no exactly how monstrous he is. His crimes include very effectively faking emotion to flatter his way up through society, burning down a library to emotionally ripple the duke (said burning also inadvertently kills an old man and he barely seems to notice. Only pausing to steal the mans skull in case it might come in useful), rewrite the ancient law of the castle to benefit himself (which in universe is a lot more serious business than it sounds) and conspiring to kill the new duke (a child), burning and drowning his teacher to death, leaving his two coconspirators to starve to death trapped in a single room and finally making the dukes sister fall in love with him purely for the power such a union would give him. He manages to do all this whole only arousing mild suspicion from other people in the castle because he's simply that good at it. When he eventually is outed as a monster he retreats into the depths of the castle and a giant manhunt is commenced to find him. He proceeds to kill any guards who find him alone and proves to be an incredibly dangerous force based purely on his willingness to kill others.
Jobe Wilkins of the Whateley Universe. At age fourteen, he's already a threat to everyone who gets in his way. He views his family as opponents. He discovered a new cure for dysentery by experimenting on unwilling prisoners. He provided a way for his father to have mine workers by developing a serum that turned people into big green Ork-like creatures. He has all the empathy of a tarantula. Fortunately, he's not a Karma Houdini.
Regent falls under this, as apparently do most of his siblings. It's implied that this is partially the result of his father's method of punishing unruly children: Flooding their mind with an overdose of terror or similar emotions. Regent does eventually develop an odd relationship with Aisha, enough that he sacrificed himself to save her.
Bitch is assumed by most people to be a low-functioning sociopath, having no regard for social customs and acting out violently. Lisa and Taylor suss out that her power overwrote her social knowledge with that of dogs. As a result she can't read human body language or differentiate between tones; this makes interacting with people confusing and she tends to fall back on violence in response.
Coil.Oh, Coil. Brockton Bay's most patient and calculating supervillain, he has most likely caused more pain (remembered by the recipient or not) than almost any other parahuman in the setting, excepting possibly the Slaughterhouse Nine. This is enabled by his power, which allows him to split the timeline and experience his actions in both simultaneously. This means he can get away with literally anything, then cancel the timeline it took place in and still feel the satisfaction of doing it. He's drugged and addicted a young girl, killed his former commanding officer for physically being in his way, and attempted to murder our protagonist several times. When Taylor and Lisa outsmarted and killed him, readers cheered.
The Spirit Thief: Sara is almost a textbook example, exhibiting all five traits described on the main page. She's completely unbothered by the fact that she's torturing sentient spirits for her own gain; she manipulates people around her to let her continue her experiments; she collects "odd" humans and wants to know everything about the spirit world; she's convinced her lab is the most important thing in the Council Kingdoms and she should always be prioritized when it comes to funding; she has no affection whatsoever to her husband and son, and considers them little more than a dead weight and another curiosity, respectively.
Judge Holden is a charismatic mass murderer who practically worships war and death. He charms and muscles his way into leading a gang of scalp hunters on a horrific and self-destructive journey through The Wild West for the apparent purpose of fulfilling his blood lust and preaching his Blood Knight ideals.