Character Derailment/Literature

Later, while on the Hunt, their group of four realizes that one of them is a traitor. Beka suspects Farmer, a man she barely knows, less than her partner of seven years and a close, loyal friend of four years, because she "just can't see" him being a traitor. Please note that Beka is notoriously shy, doesn't warm up to people quickly, and is very slow to trust people. . There's more than one reason this book hasn't sat well with many fans.
 * In a 1940 essay on Charles Dickens, George Orwell noted that Dickens derailed his characters all the time, and is "never better than when he is building up some character who will later on be forced to act inconsistently."
 * Roran from the Inheritance Cycle undergoes this after his Wall Banger (Your Mileage May Vary) slaughter of nearly 200 Mooks, wishing he could have killed more. This is nothing like how he has been previously characterized (he even angsted over the men he'd killed).
 * Lise, Madame Khokhlakov's mysteriously sick daughter from The Brothers Karamazov, eventually recovers from her affliction late in the book, right before . She goes from being a perfectly happy person in love with the protagonist to contemplating torture and murder, completely out of sync with her established character, as if just to hurt the protagonist. Most people ignore that chapter of the book.
 * Tom Sawyer started in The Adventures of Tom Sawyer as a boy who is a little too interested in pirates, but yet still very smart, genre-savvy, and compassionate. But when we meet him again in the Adventures of Huckleberry Finn he becomes a one-dimensional mockery of himself; every single of his character traits has been jettisoned except for his obsession with swashbuckling epics, which has been cranked up to twelve. This led to him hiding the fact that the captured slave Jim has already been freed just so that he can live out his twisted fantasies of a proper escape (leading to Jim being imprisoned for an extra month, being shot at, and almost lynched).
 * This Flanderization may be a result of Mark Twain's Creator Backlash against Tom's popularity.
 * In a clear case of Writer on Board, in The Land Of Mist Sir Arthur Conan Doyle has his ultra-rationalist hero Professor Challenger (who has always denied the existence of the supernatural) convert to Spiritualism. The novel is an Author Tract written following Doyle's own conversion to Spiritualism and is easily the least well-regarded (but longest) of the Challenger novels.
 * I don't know if this necessarily counts. For it to be derailment, it has to be implausible, and an Author Avatar mirroring their writer's religious conversion is nothing if not realistic.
 * Furthermore, the apparent catalyst for Professor Challenger's abrupt conversion was the death of his beloved wife, so if nothing else his abrupt change of views has a plausible explanation.
 * Straddling the line between Film and Literature is the only canonical sequel to the film ET the Extraterrestrial: The Book of the Green Planet. Any ET fan who reads it will immediately wonder why the heck ET now wants to immediately return to Earth once he's aboard the ship (the novel begins right after the film's end credits), for what reason, exactly, does ET want to get back to Elliott so bad, and why in the world is ET behaving like a jealous ex every time he gets in telepathic contact with Elliott -- who, in two character derailments for the price of one, suddenly has a crush on a girl classmate.
 * Jacob Black is introduced in the first Twilight book as a boy with a crush on Bella, fleshed out as a nice, likable guy in New Moon who becomes Bella's best friend and just wants her to be happy, and then derailed in Eclipse into a love-crazed person who sexually assaults Bella and breaks her hand. It's almost as if Meyer feared that she had made Jacob too sympathetic a Romantic False Lead and did some canon Die for Our Ship in the succeeding book to sink the Bella/Jacob ship. Jacob's characterization in Breaking Dawn is better... until he's trapped in a squicky Cleaning Up Romantic Loose Ends scheme.
 * Then there was Charlie, Bella's father and who a lot of people call the only truly likable character in the trilogy. At first, he was an overprotective father (which seems justified considering who his daughter hangs out with and his daughter being, uh, well a little too love-obsessed). Hell, he was a police officer. Then when the aforementioned event of Jacob assaulting her and breaking her hand happens, he brings her home basically to brag about it.... Which Charlie congratulates him for doing.
 * In Eclipse, the brief amount of time we see Bree Tanner leaves her very pitiable, between her being shanghaied into a newborn vampire army and sent as canon fodder against the Cullens and being murdered by the Volturi. In The Short Second Life of Bree Tanner, she goes on endlessly about how humanity sucks and she's so glad she left her human life to be a vampire, showing absolutely no acknowledgement or compassion towards the fact that she now survives by murdering people. Because, you know, any vampire who is not with the Cullens can't possibly have their condition portrayed sympathetically.
 * Deconstructed in Maus. The story continually compares the generous, brave, resourceful Vladek Spiegelman who survives the Holocaust to his present self, who has inexplicably devolved into a cranky pain that makes life miserable for everyone. Part of this (non-fictional) account deals with the author's issues and incredulousness at the difference between his father's behavior then and now. The story also rejects his Freudian Excuse of behaving the way he does, noting that other Holocaust survivors didn't become the bitter shell he is now.
 * It should be noted that the portrayal of Vladek as he was during the Holocaust could be a case of an Unreliable Narrator; the only source of information we have is Vladek himself, and attention is drawn several times to the fact that Vladek's memories sometimes contradict themselves or other eyewitness accounts.
 * Also, it is debatable whether Vladek's post-Holocaust misanthropy is truly a derailment from what he was during it; there is never any question that he loved Anja (his wife during the Holocaust, who committed suicide a few decades after it was over) far more than Mala (his wife at the time of writing), so it makes sense that he would be far more compassionate towards Anja. Old Vladek also shows resourcefulness, but because it is unnecessary in his time it comes across as simple miserliness. There are also hints from Vladek's possibly rose-tinted memories of himself that suggest he might have been somewhat domineering and lacking in sympathy even then.
 * Count Hasimir Fenring in the Dune prequel trilogy books. He goes from the only friend the emperor has and actually a fairly decent (though very dangerous and plotting) guy to a huge jerkass with no loyalties or real redeeming characteristics. He is also rather incompetent, and apparently in the later sequel books tried killing Paul Atreides for no real reason when you consider he could have done so in the original book easily enough himself. Also the Emperor turning from a slightly vicious but competent Emperor to a rather stupid tyrant in the same prequel books.
 * The Vampire Diaries: The Return: Nightfall by L. J. Smith was a trainwreck. She changed the universe of the story mid series, and ruined the Ensemble Darkhorse.
 * Let's put it like this. The publishing company fired her from her own book series (they actually commissioned her to write it way back before it was televised, and consequently own the rights).
 * Warrior Cats: Double subverted in Twilight when some of the characters are confused about how Onestar became such an ass overnight. It's at first dismissed as him asserting WindClan's independence, but it's still ongoing seven books later. In fact he's even worse now.
 * Actually explained in Cats of the Clans, where it's stated that Onestar knew that, as leader, he couldn't be known as "Firestar's kittypet, the one who'll roll over so that Firestar can tickle his tummy." He's not happy about, but he knew that if he was going to be accepted as leaders (especially under the circumstances), he was going to have to prove he wouldn't bow to Firestar's every whim.
 * Remember when Anita Blake Vampire Hunter was a tough, sarcastic but interesting young woman who hunted vampires and played in the sandbox with various preternatural critters like werewolves, wereleopards and the like? Up until The Killing Dance, she was also a Celibate Hero. Then she slept with a vampire. And then she slept with a werewolf. No big deal, she just had to choose between the two of them and--oh no, there's this thing called "the ardeur" that means she has to have sex every few hours or she will in fact die. And then she began an insufferable, short-tempered God Mode Sue who wants everything to go her way all the time or she'll kill you.
 * Admittedly, the new whore!Anita version was unveiled in "Narcissus in Chains" fully, a few books after "The Killing Dance," complete with that newfangled aurdeur. The fact that the author had divorced her husband and "upgraded" to the younger president of her fanclub? COMPLETE coincidence, of course. One has to wonder if it means the author went through her own derailment, or was merely hiding it well.
 * Karen Traviss loves to tell readers how Jedi are incompetent and evil and Mandalorians are awesome. Since the Star Wars EU is a shared setting and characters established by other authors are fair game (though it's apparently considered bad form to handle them without permission), Traviss cameoed Scout as someone who the Jedi disliked and rejected because her powers were weak, heavily implying that she became a Mandalorian. One problem: Scout's powers were weak, but she was inventive and ridiculously determined to overcome that, which the Jedi and especially Yoda respected. Traviss has said herself that she doesn't read anything from the EU; she gets people to provide characters to use and basically ignores anything she doesn't like.
 * And in Traviss' notes for the now canceled Imperial Commando 2, she stated that Scout would have remained a Jedi with Jedi Master Djinn Altis' sect of Jedi in-hiding. The only thing that would have changed is Scout being adopted by the aformentioned Mij Gilamar as his daughter, and not a problem in Altis' family-friendly Jedi sect.
 * Thus turning Scout to the biggest moron in the entire galaxy since her back story as a weak-in-the-force-but-detemind-Padawan who struggled so much to prove she could be a Jedi complete pointless since she could just joined that group of Jedi!
 * Two glaring examples from Legacy of the Force were Jacen Solo and Tahiri Veila. Jacen went from being an intelligent and highly moral Jedi to a raving mad Sith Lord seemingly for no other reason than because he learned from a very questionable source that one of his teachers had once been Sith herself (said teacher's philosophy was rather darker than that espoused by most Jedi, true, but Jacen himself had never shown any real sign of buying in to her more brutal teachings himself, and even these were often diametrically opposed to orthodox Sith philosophy anyway). This was intended to be an example of Jumping Off the Slippery Slope, but it's so abrupt and the resulting character so different from the Jacen EU fans were familiar with that it was very jarring.
 * Tahiri Veila, Jacen's apprentice, had it if anything worse. At the end of the New Jedi Order Tahiri was a damaged but strong young woman who had clearly passed through her trials a stronger person. In LOTF she's suddenly regressed to how she was immediately following the death of her love, Anakin Solo, and is willing to do anything for Jacen (up to and including murder) if he'll use the Force to show her visions of Anakin from the past. Also, the fact that Tahiri was effectively half-Yuuzhan Vong thanks to a Shaper's experiment was greatly played up in New Jedi Order, but ignored almost completely in Legacy of the Force.
 * The really annoying thing? Both of the above characters were canonically established as having darkness in them- it would have been entirely possible to turn one or both evil much more tragically without simply flipping a switch in their personalities, but said flipping is what ultimately happened.
 * There's an explanation for this: Originally, it was planned that Anakin would be the one who fell, in a mirror of his grandfather's own descent, but George Lucas decided it was too confusing, and had them switch it. So Jacen almost literally became Anakin.
 * Ho boy, does this ever happen in the eleventh book of Everworld to . K.A. Applegate somehow derailed, "Ambitious, intelligent, controlling, Dangerously Genre Savvy True Neutral Visionary Villain Magnificent Bastard with a taste for power" into "batshit insane, power-mad, Chaotic Evil Genre Blind Bad Boss Evil Overlord." Her whole character in the later half of the book reads like a fanfiction written by someone who had only a shaky understanding of the character, and completely ignores the extensive backstory and characterization that   got two books ago in Inside the Illusion. Of course, given Applegate's tendency to have books "ghostwritten", this might actually be what happened.
 * Skif from the Heralds of Valdemar series goes from a streetwise, snarky, and incredibly skilled former thief to love-starved twit in the Winds series.
 * Justified in that he's suffered severe emotional trauma and this is somewhat-less-than-healthy coping strategy. After he finally gets some therapy, he goes back to normal.
 * In the Chronicles of Narnia, Susan is initially portrayed as the most mature and reasonable Pervensie sibling. By The Last Battle, in a highly controversial (and in some people's eyes, sexist) development, she appears to have become mainly focused on going to parties and gossiping, and no longer believes in Narnia.
 * Actually, she'd already shown signs of it in Prince Caspian (although seeing Aslan again shocked her out of it) and it was mentioned in the Voyage of the Dawn Treader on account of being the 'pretty one of the family' she got to go on a long trip to America with her parents (which might have contributed to it). This of course brings up Unfortunate Implications concerning Lewis' views on the US...
 * A baffling case, a group of Harry Potter fans try to claim this happened with Hermione in books six and seven. This is likely because after Harry Potter and the Half-Blood Prince, they could no longer pretend Hermione didn't have feelings for Ron.
 * The "problem" with that point of view though is not in the opinion of people for or against, but in that the author spent a whole five books not only showing that Hermione didn't have feelings for Ron, but acting completely disinterested when Ron tried to show how he felt towards her, no matter how "subtle" Ron's overtures might have been at times. Combined with the fact that she was put in situation after situation with Harry and showed how she reacted to him as opposed to Ron (most explicitly shown in book five). So to suddenly in book six have her gaga for Ron, regardless of whether any individual reading liked that developement or not, was indeed character derailment.
 * A much more reasonable case could be made for Nymphadora Tonks. She's presented as a strong, capable, independent woman who devolves into a much weaker character who begs Remus to go out with her.
 * The Provost's Dog: Somewhere between books two and three, of the  went from being a friendly, widely-liked, upstanding man  to a grumpy, misanthropic man who was barely civil with his.
 * Beka suffers from this as well, and, by proxy, her friends. When the book opens, she's at her betrothed's funeral. Said betrothed was verbally and possibly emotionally abusive, and she put up with it. It's implied that her extremely protective friends did nothing about it, and that her extremely protective god-like constellation cat neither said nor did anything about it, despite the fact that he'd made his dislike of Dale, her previous love interest, very clear -- and Dale was nice.