Many characters in Jack Vance's books, most notably Cugel the Clever, who for most of his two books will steal from, exploit, murder, or in some other way take advantage of anyone who has something he wants, or, really, even those who do not. Cugel is squarely the protagonist and Vance is a master of neutral treatment — Cugel's un-judged behaviour can be quite breathtaking.
By Work:
In the Age of Fire series, Infamia takes the cake. She's betrayed her mate, abandoned her other mate, defecting from her new employers after leaving in exile, then betraying her new king, and then betraying her mate again (who was the first one she betrayed). Subverted in that, except for the first two incidents, she was possessed by the Red Queen.
Vissers 3 and 1 in Animorphs. Probably other officers of the Yeerk army as well, but these two are most prominent, constantly working to undermine each other's position, even if it harms the greater cause and helps the Animorphs.
This seems to be a deep cultural practice of the entire Psychlo race in L. Ron Hubbard's Battlefield Earth. They spend so much time blackmailing and backstabbing each other it's amazing their species manages to run an inter-galactic empire. Terl, the Earth franchise's security chief is a toxic example even amongst this crew: he needs to betray so badly it at some level it surpasses rationality. It turns out that Psychlos have bad wiring in their heads.
Belisarius Series: The eunuch Narses has a genuinely pathological form of this. For his first betrayal he, Grand Chamberlain of the Roman Empire and the only high official the Ruling Couple completely trusts, commits to a conspiracy that would cost the life of the closest thing he will ever have to a daughter to his credit, when the whole thing goes south he goes out of his way to save her before escaping) in the hopes of becoming The Man Behind the Man for Justinian's replacement. He hates himself for it and is convinced he will be dead of old age (and damned to Hell) in a few years no matter what, but he just can't stop. At the end of the series, he ends up betraying the Big Bad. His master immediately sends him to China to take up new opportunities, coincidentally giving him an entirely new scope for his intriguing abilities. The other option, they both know, was just to kill him; he's that dangerous.
The Black Arrow: Sir Daniel Brackley changes sides so many times in the course of the War of the Roses that not even his protégé Dick can tell what side he is currently on when asked.
"Come, now, will ye read me a riddle?" returned Clipsby. "On whose side is Sir Daniel?" "I know not," said Dick, colouring a little; for his guardian had changed sides continually in the troubles of that period, and every change had brought him some increase of fortune. "Ay," returned Clipsby, "you, nor no man. For, indeed, he is one that goes to bed Lancaster and gets up York."
The Black Swan: Uwe toes the line between this and Manipulative Bastard. He allows Queen Clothilde to believe he is helping her set up her son for a tragic 'accident' which will let her keep the throne for life — in reality he is setting her up for Baron von Rothbart to destroy her. Unfortunately for Uwe, the Baron rewards him as a traitor deserves.
In the Chung Kuo novels there are many betrayals — the upper levels of society run on Machiavellian scheming — but the supreme Wei Chi Master Howard DeVore outdoes them all. At first his betrayals seem to follow the logic of power, and he gets away with them all — he's slippery — but in the end, he betrays everyone, that is, the human race.
The Clique: Over the course of 13 (14 if you count the prequel) books the middle school girls, including Claire, backstab each other at least thrice. Prize goes to Massie and Alicia, who backstab each other so much it's not hard to lose count.
Codex Alera: Aquitainus Invidia will betray anyone and everyone in order to secure greater power for herself and, later, survival. Any character who has dealings with her not already possessing it quickly develops enough savvy to try to take Invidia's sudden but inevitable betrayal into account. In the last book, The Vord Queen doesn't even have any emotional reaction at all when it's her turn to be backstabbed. She explains that Invidia IS this trope and doing anything else simply would not be Invidia.
"Truces in this land are made to be broken," he answered grimly. "He would break his truce with Jihiji. And after we'd looted the town together, he'd wipe me out the first time he caught me off guard. What would be blackest treachery in another land, is wisdom here.
The Count of Monte Cristo: Fernand Mondego achieves success through betrayal. First, he participates in setting up Dantes so he can have Mercedes for himself. Then, during the Napoleonic Wars, he and his superior officer both desert Napoleon at the right moment, earning promotions from the new Royalist Regime afterward. Then, as a sort of mercenary in the Greek Wars of Independence, he is a well-paid commanding officer under Ali Pasha who he betrays to the Turks. Not only does he gain a fortune for this treason, but back in France everyone thinks he's a war hero and he ends up a general.
The way to get ahead at Unseen University is "by way of dead men's pointy shoes." In other words, kill the guy above you and steal his shoes and hat. Rinse, lather, repeat. Since the elevation of Mustrum Ridcully as Archchancellor, this process has been halted, by virtue of him being virtually unkillable, resulting in a lot more permanency among the other senior wizards as well as backstabbing decreases.
Played straight in The Last Hero with Evil Harry Dread, who has a(n im)moral obligation to betray the heroes. This is not only not frowned upon, but actually applauded by them. (It helps that there's "The Code": He'll act in certain ways, and they'll respond in certain ways. Everyone lives to fight another day. One of Harry's complaints is seeing the newer heros not playing by the same rules.)
Lord Hong in Interesting Times. He helped along the revolution himself just so he could start a counter-revolution, he more-or-less cooperates with the other feudal lords while maneuvering for the crown, he has his minions killed after explicitly promising them to not give any orders to that point, he has no problem telling his soldiers lies which run exactly contrary to what they were told a few hours ago (and expects them to believe him!) and last but not least, is very clear on it that it's fine for a few hundred or thousand of them to die, because that's what they are for. Oh, and he had the emperor killed (stabbed!), but that's part of the power routine.
Peter Hayes from Divergent consistently betrays his allies at least once per book, regardless of whether it benefits him or not. It's so pathologic that by the third book he has a Heel Realization and elects to wipe his memories so he can stop betraying everyone.
Finally you have his (arguable) betrayal of himself when he undoes everything he's been working towards in order to save himself from eternal loneliness.
Raistlin's half-sister Kitiara steps up to the plate:
She betrays Tanis by seducing his best friend Sturm.
She betrays all of the Companions by not honoring her oath to them and by joining the Dragonarmies.
She betrays Laurana by luring her to a false parley and kidnapping her.
She betrays Raistlin and Iolanthe by trying to kill all wizards.
She betrays Tanis again by offering to spare Laurana when she has already decided to give the elfmaid a Fate Worse than Death.
She betrays Ariakas by plotting to overthrow him.
She betrays Lord Soth by letting Tanis take Laurana.
She betrays Raistlin again by having Lord Soth try to kill Crysania.
The Order of the Blackened Denarius is a collection of no more than thirty individuals who possess a coin that holds one of thirty Fallen Angels who were involved in Lucifer's war against Heaven and banished along with Lucifer. They tend to betray each other every so often, working to undermine or outright sabotage the greater goal of corrupting and destroying humanity. It is when they can put their issues aside for a short time that things get bad for humanity. The last time two faction leaders actually got together for a time led to the Black Plague in Europe.
One member of this collective is Lasciel. She is known by her monikers of Webweaver and the Seducer. She wasn't banished from Heaven just for siding with Lucifer, but rather because she tried playing both sides against each other to come out on top no matter what. When things settled, God did not take favorably to this action and kicked her out too.
Their lack of unity and backstabbing nature is the reason Lucifer chose these thirty Fallen to be placed in these coins. He had convinced each one of them they were better off fighting God and lost big time. It was only a matter of time before some of them rebelled against him to take him down. So, he sent into the coins the most dangerous of the Fallen to keep them away from his position in Hell.
An entire society (at least, the ruling class) runs on a combination of this and Klingon Promotion in Empire of the East by Fred Saberhagen, with everybody stabbing everybody as soon as there is an advantage. Exemplifying this is Lady Charmian, whose backstab against her newlywed husband (for the offense of leering at a chambermaid) ends up costing her father his life, through a long series of circumstances. She then arranges for her disgraced husband's rescue from the rebels, arranges for him to duel with her current lover (expecting him to lose), sets him up to be killed by a demon when that fails, backstabs numerous rivals for power, and eventually betrays her husband again after his Heel–Face Turn to the rebel side. But somehow she never quite goes through with killing him when she has the chance to do it herself.
Mercenaries, particularly the leaders of the Thousand Swords, and particularly Nicomo Cosca, are known to switch their allegiance or simply abandon their employers when it is profitable or expedient to do so.
In Best Served Cold, Duke Rogont has purposefully sabotaged the battle plans of his own allies in the League of Eight to diminish their power and ensure his supremacy once they defeat their mutual enemy Duke Orso. However, he diminished his allies so much that by the time Rogont is ready to fight for real, Orso is much more powerful than the remaining members of the League.
Flashman inevitably gets to see any conflict from both sides due to getting captured and/or turning his coat.
Harry Potter: According to Pottermore, the Ravenclaw house has a problem with this at times. Though since the information came from the Slytherin Prefect, it must be taken with a grain of salt.
A straighter example is Peter Pettigrew. He initially befriends Sirius Black, Remus Lupin and James Potter primarily to be on the side of the “cool kids on the playground” (although Lupin was also the only person to be consistently nice to him). Then Voldemort starts gaining power and despite the fact that he’s now a member of the Order of the Phoenix, Pettigrew decides that Voldemort will give him more power and becomes The Mole, only for his betrayal of James and his family to backfire and force him to hide. Although he more or less remains on Voldemort’s side, even Voldemort knows that the instant Wormtail can get a better deal elsewhere, he’ll turn on Voldemort and takes precautions against the moment when Wormtail would betray him — or even appear to do so.
Journey to Chaos: Dengel is known for switching sides when advantageous. In his own words, "Unlike my brethren, I know when to make deals." This is why the Big Bad knew that his We Can Rule Together attempt would succeed in the climax.
In Known Space, Pak Protectors were in a perpetual state of war, because everyone was biologically hardwired to serve the short-term interest of its own clan. Even when clans tried to be allies, the protectors would instantly, involuntarily backstab each other as soon as an opening appeared. In The Ringworld Engineers, a protector is friends with the main characters and needs them to save its whole world, but finds itself trying to kill them anyway because they are a threat to some of its own relatives.
The Last Adventure of Constance Verity: Of all the ex-boyfriends Constance Verity has the most trouble getting over, it's the ninja-for-hire Hiro. Whenever they team up for something, he will, without fail, leave her hanging (literally over a crocodile pit in one instance) while he stealths his way out of the situation without her.
In the Lensman novels, the Boskonian culture, spread through two major galaxies, runs on this trope. Everyone moves up through assassination and/or betrayal of their superiors. And they get away with it, as long as they protect themselves from others assassinating/betraying them because that's how you legitimately advance in their culture. Kim Kinnison goes undercover and works his way up to supreme dictator of an important planet and all its dependencies by a series of betrayals and assassinations, and he's widely admired and respected for this.
Ludovico in Leonardo's Swans. He does this both to his wife and his political allies.
The society in Cyril Kornbluth's classic dystopia The Luckiest Man in Denv operates this way. In particular, the generals appear to spend more time intriguing against each other than prosecuting the war against Ellay. The protagonist, Reuben, is also no slouch when it comes to backstabbing his own superior officer.
In the Malazan Book of the Fallen, backstabbing is part and parcel of being an Eleint or a Soletaken Eleint. The reason given is that draconic blood is chaotic by its nature and cannot abide its own proximity. As Silchas Ruin explains it, to the Eleint "any notion of community is anathema" and they see any world as a feeding ground which exists to sate their innate megalomania. To drink draconic blood and become a Soletaken Eleint means gaining a taste for betrayal and a lust for power for their own sakes and only a handful of people are said to have ever overcome this urge, most of whom were several generations removed from their draconic ancestors.
Metaltown has Jed Schultz, who's on no one's side but his own and is willing to stab anyone in the back so long as it serves his needs.
Alexander Belanger in Pale, an Augur specializing in Strife practices. Alexander revels in causing chaos and uncertainty around him, which is dangerous enough when he's a friend and worse when one is a student at his school, the Blue Heron Institute. Once put his most important friendships on the backburner so that he could truthfully claim to his acquaintance Lawrence Bristow that he was his closest friend, so that Bristow would cry on his shoulder and Alexander could collect his tears as spell reagents for when he inevitably betrayed Bristow.
Slagar the Cruel elevates this to a business model: gather a crew of slavers, kidnap some innocents and sell them to the Kingdom of Malkariss, manipulate the crew into killing each other so he can hoard the profits, rinse and repeat.
Lu Bu manages this in truly appalling fashion. The Reader's Digest version would go: murdered his adoptive father for a horse, murdered his next adoptive father for a 16-year-old girl, became a rebellious warlord, betrayed his friend Liu Bei, and finally tried to sell his services to his sworn enemy Cao Cao. Cao, being a Magnificent Bastard, said simply, "Strangle and expose."
Cao Cao did it after asking Liu Bei (who was working under him at that time, see below) what to do with Lu Bu. Liu Bei lampshaded this trope for him: "Don't you remember what happened to Ding Yuan and Dong Zhuo?" (Lu Bu's two previous adoptive fathers, both killed by him)
Liu Bei himself is an ambiguous case. He's talked up as a great hero, but everyone he ever works for (except Cao Cao, who suffered a series of humiliating defeats) dies, normally after willing their entire empire to him. You start to wonder just how reliable the narrator is.
Wei Yan was portrayed as one, lampshaded by Zhuge Liang: He killed his previous master and surrendered the city to Liu Bei (A while ago he betrayed another master when said master was fighting against, guess what, Liu Bei). Zhuge Liang urged Liu Bei to killed him, citing "The bones of treachery grows in his brain". Liu Bei didn't kill him, and he remained under Shu service as an important general for a couple of decades. He committed treason again after Zhuge Liang died, though.
Safehold: Everyone who had dealings with Grand Duke Zebediah was fully aware that the question wasn't whether Zebediah would betray them, but when. When it's Cayleb's turn to be the one Zebediah is swearing fealty to, he promptly puts Zebediah under SNARC observation ... and sure enough, collects enough evidence of treason to justify executing Zebediah and putting someone honest in his place.
The villain, Achilles, in Orson Scott Card's Shadow Puppets trilogy. By the end, he's betrayed Russia, India, Thailand, China, and the Hegemon. Also, he kills anyone who's ever seen him vulnerable, including people who help him out of said situation.
Petyr "Littlefinger" Baelish, the resident Magnificent Bastard. He's actually pretty jokingly upfront about being a chronic backstabber, but no one takes him seriously until a bit too late. He allies himself with Eddard Stark, causing him to believe that he had the resources to move against the Lannisters. But then when it comes time to act, Baelish betrays Stark to the Lannisters. He then frames Tyrion Lannister for the murder of his nephew Joffrey, causing House Lannister to tear itself apart — and making way for his new allies, the Tyrells, to take control of Westeros. With each successive betrayal, Baelish's own personal standing is increased, going from an unappreciated civil servant to the ruler of two of the Seven Kingdoms, and with Stark's eldest daughter, Sansa, as his protegée. And then we learn that the murder that made Stark want to get revenge on the Lannisters (Jon Arryn's) was committed by Baelish all along, having manipulated his wife Lysa into doing it. That said, a lot of his betrayals have relied on being very lucky, his plans could easily have gone wrong, and when Ned first met Petyr his initial reaction was to not trust him, but his wife Catelyn didn't realize how corrupt and resentful her foster brother had become and told her husband he could be trusted.
Everyone assumes this of Jaime Lannister "the Kingslayer", ever since he killed King Aerys II while serving as part of his Kingsguard. Aerys was planning on burning down the entire capital city and the entire population thereof rather than allow his enemies to conquer it; Jamie only killed him to prevent this from happening. When he gets a POV chapter later in the series, we see that he's completely aware of his reputation and enjoys utilising it to his advantage.
Generally the norm amongst sellswords, many of whom will take anyone's money and fight for them. Until someone else turns up who offers them more money or looks like they might win. Brown Ben Plumm, captain of a free company, is a notable example, having betrayed his former employers to defect to Dany's side, and then defected right back when things stopped looking so rosy.
House Bolton has the motto of "Our Blades Are Sharp" ostensibly about their traditional family practice of skinning condemned prisoners. However, sharp daggers work just as well on so-called friends and allies — as the family has demonstrated for centuries. And... occasionally.. family, too. Note, there are currently only two acknowledged male Boltons, and one is a bastard who luckily inherited when his legitimate half-brother ever so suddenly died. Yeah.
There was the historical example of Hugh the Hammer and Ulf the White, a pair of dragonseeds (Targaryen/Velaryon bastards) who were trained to ride dragons during the Dance of the Dragons. Initially siding with Rhaenyra Targaryen's blacks, they defected to Aegon II's greens during the First Battle of Tumbleton, which contributed to the blacks losing that battle. Then they felt slighted by Prince Daeron's ostensibly minor rewards for them, and decided that they wanted to become the King of the Seven Kingdoms. Eventually, their attempted coup was heard by the greens, who decided to eliminate them both, but the distraction enabled the blacks to smash the greens during the Second Battle of Tumbleton. They have since been branded "The Two Betrayers", and their infamy was unfortunate in hindsight since they validated the Westerosi view of bastards being evil, scheming traitors.
Lily, of Austin Grossman's Soon I Will Be Invincible. In her Backstory, before the events of the book, she was sent back in time to Set Right What Once Went Wrong, did so, then decided to attempt to undo her changes so that she could go home. (This Backstory is revealed to be false. She was originally Lois Lane to the Superman-likeCoreFire before getting empowered and dumping him.) She became a supervillain, eventually hooking up with villainous Dr.Impossible, then left him for his Arch-Enemy, the superheroCoreFire; as the story opens, she is just being recognized as an official member of CoreFire's team, the New Champions. She then provides Dr. Impossible with the last Plot Coupon necessary for his latest Doomsday Device. Doing so is what saves the world from the disaster described in her Backstory, and lets Dr. Impossible beat the snot out of CoreFire. Then she backstabs Dr. Impossible again to save the world yet another time, before chewing out both him and CoreFire and leaving them tied up to the same post. Even at the end of the series, it's clear the only side she's on is her own, and quite effective at it. Ironically, she's transparent.
Star Wars Legends: The X-Wing Series' Ysanne Isard. Nominally always working for the Empire, but after the Emperor died, she was just working for herself. Despite constantly insisting she had no desire to replace the Emperor, her actions made it clear that she was egotistical enough to consider working for herself and working for the Empire to be the same thing. Later in the series, Baron Soontir Fel and Gara Petothel are both accused of this. It's untrue on both counts.
The Stanleys in The Sunne in Splendour. They keep betraying people even when it doesn't actually improve their situation. Since this is a historical novel, that was Truth in Television. The Stanleys were known as being turncoats.
In the present, the group remark on the stupidity of this trope as a stereotypically villainous act, since adhering to it is what led to Evil being mostly wiped out. The villains note how backwards it is to be at the throats of your own allies, even when in a position where you can trust no one. They themselves manage Teeth-Clenched Teamwork to get through the adventure, eventually growing into actual trust, albeit nearly getting into a real fight once until Kaylana coolly talks them out of it by noting this would be self-destructive.
A Civil Campaign: Byerly Vorrutyer, the man-about-town and general political stirrer. He has motives so indiscernible that it's very hard to tell exactly who he's actually betraying, and whether he's a double agent, triple agent... or what, really. Actually working for the government (but, rather like Miles, extremely prone to exceeding his orders... and with a somewhat blasé attitude towards the safety of others). We think.
Ivan: You've lied and you're lying, but I can't tell about what. You make my head hurt. I'm about to share the sensation.
In The Vor Game, we meet a more pathological version in Commander Cavilo. Having already vamped her way into command of a mercenary warfleet, she gets hired by a planet during a staredown with a rival, sells them out to the Cetagandan Empire, then backstabs both the Cetagandans and her own fleet for a chance at seducing the Barrayaran Emperor Gregor (who had slipped out of The Chains of Commanding after a drunken, halfhearted suicide attempt) into making her his consort. It is mentioned (though not by name) as being her downfall. If she had stuck with one plan, any plan, she could have probably pulled it off. But she's unwilling to follow through when she thinks something better comes along.
Miles himself seems to suffer from a variant of this disorder (which is lampshaded in the series, especially The Vor Game and Memory). Rather than intentionally betraying allies and neutrals, he makes commitments (implicit or explicit) which he later can't fulfill without breaking another one. (He doesn't want to betray people, and he generally manages to juggle responsibilities and deceive people until he finds a solution. However, his skill at avoiding having to follow through with the final outright backstab doesn't prevent the lead-up from being its own form of betrayal.) The pattern is most clearly (and avoidably) showcased in the first book featuring him, The Warrior's Apprentice.
The Warlord Chronicles: Already King of Siluria, Gundleus is set to marry Uther's daughter in the wake of Uther's death and be the regent for Uther's infant grandson, who will be the future High King. Instead, Gundleus gets greedy and decides to shoot at becoming High King himself, murdering his wife to be and attempting to kill the baby as well. After Arthur captures him alive and treats him well, Gundleus promptly sides against Arthur in the next round of warfare among the British kingdoms when it looks like Arthur is going to lose. Oh, and in addition to killing his wife and attempting infanticide, Gundleus also rapes another character and rips out her eye.
Worm: Affects several people and organizations, but none more so than Coil. Over the course of the series (plus flashbacks), he's manipulated just about every major faction and even individual characters before stabbing them in the back, whether they know it or not. After the Undersiders and the Travelers take over Brockton Bay for him, he tries to kill our lovely protagonistmultiple times, and plays all the others like a fiddle until they've outlived their usefulness. Hell, the man got his start by killing his commanding officer on the Nilbog mission, literally shooting him in the back for taking too long to climb a ladder.
Lord Gro from E.R. Eddison's The Worm Ouroboros had a bad case of this, due to his desire to be fair and support the underdog. Eventually, it did cost him his life when he started killing soldiers on both sides in the middle of a battle to show there were no hard feelings.
