Paradise Rot: Desmond is a very polite, small, and outspokenly gay zombie that turns out to be just as good at this Rambo stuff as Oscar.
In Dragon Bones, there are several examples. Lampshaded with old nobleman Haverness, who has a reputation for being honourable to a fault, very traditional, and the only one at the decadent court who takes oaths really seriously. He is known to be absolutely loyal to the king. Until king Jakoven makes it clear that no, he will not provide help to defend Haverness' homeland Oranstone against bandit hordes. With which he breaks his side of the oath, and frees Haverness to start a revolution. Haverness is a good fighter and strategist, and so is his daughter.
And then there is Oreg, who seems to be a frightened youth of seventeen, and is very polite. Only that he's actually a powerful mage. And has been trained as assassin. He's still The Woobie, as he's an immortal slave, bound by magic too powerful even for him to break. He's freed when Ward kills him at his own request, and later returns as a dragon. Fortunately, Ward is nice to everyone, otherwise that could have ended badly.
She's like a small, furry animal. "And the trouble with small furry animals in a corner is that, just occasionally, one of them's a mongoose."
"Magrat was always the nice, kind, soft one... who'd just fired a crossbow through the keyhole."
Magrat, on learning the new king who doesn't respect witches has commissioned a play discrediting them, suggests "We should fill his bones with hot lead!"
Though not as obvious as Magrat, Nanny Ogg is definitely someone you don't want to piss off. Contrast to Granny Weatherwax, Nanny is the nicest person you're likely to meet (unless you're one of her daughters-in-law), but pushing her is a very bad idea, evidenced by her threatening the Elf king.
"A mind like a buzzsaw behind a face like an old apple. She may actually be more powerful than Granny."
"And don't go thinking I'm nice. I'm only nice compared to Esme, but so is practic'ly everyone."
There's also Carrot Ironfoundersson, a six-foot-six tall dwarf (adopted human, of course). He is perfectly kind, lawful, and incorruptible in a city that is far from any of the above, always sees the bright side of things, and is friendly to everyone he meets. He can convince bloodthirsty desert tribesmen not to charge (a feat which one who knows said tribesmen compares to "Making water run uphill"), get rival gangs of street urchins to play football, and have a friendly chat with a dictatorial if cultured tyrant. He's also strong and skilled enough to fight hand-to-hand with an alpha male werewolf and survive (in The Fifth Elephant), has a punch that will knock out a troll (those are guys made of solid rock, for those keeping score), and along with having a sword sharp and strong enough to do it, push a sword through a stone pillar like a knife through butter (in Men at Arms). It is not a good idea to give him a reason to take the gloves off, as the man standing between Carrot and said pillar found out.
Oddly enough, Carrot also subverts the trope by his buttons not being pushable by most personal methods. When his girlfriend/lover/person-with-whom-he-has-an-Understanding is kidnapped (in Jingo) and skips town (in The Fifth Elephant), he informs the proper authority before trying to go after her. This is because he believes with all his heart that personal is not the same as important - and this makes him all the more dangerous. How many heroes have been dissuaded from doing in the bad guy by a convenient personal appeal?
Remember, Boys and Girls; "If you have to look along the shaft of an arrow from the wrong end, if a man has you at his mercy, then hope like hell that man is an evil man. Because the evil like power, power over people, and they want to see you in fear. They want you to know you are going to die. So they'll talk. They'll gloat ... A good man will kill you with hardly a word."
At one point Angua asks him if he'd kill her if she'd let her werewolf instincts get the better of her. He ponders the question and replies that yes, he would. It was the answer she wanted to hear, though.
And Mort in Mort. Death's controlling ways and preference for extreme consequences causes him to challenge the Grim Reaper himself in one-on-one combat. "My name is Mort, you bastard!"
Otto Chriek. He's a Friendly Neighborhood Vampire who maintains a Count von Count style persona to look as unthreatening as possible, belongs to a vampire teetotaller's society, and is happy to be left to practice photography in peace. But fuck with people he cares about and he will very gently remind you that he is still, in fact, a vampire.
"I never liked zer damn cocoa anyvay."
From the same book (The Truth), Sachrissa get a mad gleam in her eye when there's a reason for her to get nasty. The narration notes that is worse in people who have always been nice, as they have much more bad behaviour stored up than those who let it out regularly.
Apart from those already mentioned, add in Angua, Detritus, A.E. Pessimal, and ooh, probably many of the rest of the watch.
In Discworld, Death (or rather, Death) is actually a very nice guy. Unless you manage to upset him. The Auditors have managed it several times, and the results tend to be rather spectacular.
The senior wizards of Unseen University are generally rather nice fellows (although they tend to seem quite dotty to outsiders) interested in little more than eating colossal meals and drinking enough high-quality booze to stun a herd of elephants. Removing the social and power restrictions turns each one of them into a Person of Mass Destruction, dedicated to the annihilation of all other wizards. Threatening them or anything they regard as theirs (including causing their preferred history in their pet universe to go off track) will result in them calling down rather worse than hellfire on you.
Farmer Boy by Laura Ingalls Wilder recounts how the older boys at Almanzo's school have made a yearly practice of delivering a one-sided beatdown to their teacher, hurting them badly enough that one of the previous teachers died. This year's teacher is small, nice, soft-spoken Mr. Corse, and Almanzo dreads having to see what the boys from Hardscrabble Hill are going to do to him... until the big boys actually show up and Mr. Corse demonstrates that he's ready for them, literally whipping them all the way out of the classroom with a fifteen-foot blacksnake whip.
Jake of The Dark Tower. A nice normal little kid - but capable of being as ruthlessly efficient a killing machine as any other Gunslinger when necessary. To say nothing of what happens if you hurt his friends. To the point where he actually pulls his gun on a motorist for almost running over Oy
Joshua from Dora Wilk Series. Usually, he's Shrinking Violet, down-on-his-luck angel in the shadow of his more outgoing friends Miron and Dora. But he's also one of the few angels who can Manifest, and when he does, better for you not to stand between him and his target.
Near the end of A Storm of Swords, Tyrion Lannister finds out that his horribly abused first wife Tysha, who he thought was a prostitute, actually loved him. This is the last straw, and he swears vengeance on his family and kills his father (on the privy, no less) along with his former concubine (who had humiliated him during a show trial). *And* he tells his older brother Jaime that sooner or later he'll kill him too, for obeying their dad's orders of following the charade.
Cute Bruiser Arya Stark. Remember, the precocious little tomboy who just wanted to be treated equally with her brothers? Yay, you do not want to fuck with her, especially after she starts going valar morghulis on anyone who gets in her way.
Jaqen H'ghar. To clarify, Arya joins up with Yoren and a party of criminals brought out of the king's dungeons to serve on the Wall. Three of these are considered so dangerous that they're kept in cages in a cart. One is a shameless rapist who's always harassing people, one is a mute cannibal who's always snapping at people, and one is a soft-spoken and unfailingly polite man with a strong personal code of honor. No points for guessing which one is the most dangerous. Even the other two are afraid of him.
Daenerys Targaryen is, generally speaking, one of the most compassionate and well-wishing characters in the series, especially where the weak and abused (slaves, children, etc.) are concerned. Hurt them or the people she loves, however, and you are likely to die a horrible death, probably involving a great deal of fire. She doesn't take too kindly to betrayal, either.
Roald Dahl's Matilda is one of the nicest children you could wish to meet - as long as you don't make her mad.
Tom Clancy's Ryanverse has John Clark, an ex-Navy Seal and Intelligence operative. He is normally a nice guy, but if you mess with him or anyone close to him, you will know pain. In Without Remorse, after the accidental death of his wife, his next girlfriend is a former prostitute/drug mule. When her former employers kill her, John Clark then proceeds to kill every one of them, and torture the worst of them with a pressure chamber. In The Sum of All Fears, some neighborhood punks harass a local convenience store owner under his protection; he and his CIA protege beat the living snot out of them.
He is best summed up by:
John: "I am the most even tempered person I know."
Jack: " Yah, they're dead before you're mildly annoyed"
Harry Potter has at least one lovely example of this. Molly Weasley is normally a pretty sweet-natured lady. However, when she's angry, her husband and sons are all terrified. How did J. K. Rowling describe her in The Chamber of Secrets again? Oh, right:
Mrs. Weasley was marching across the yard, scattering chickens, and for a short, plump, kind-faced woman, it was remarkable how much she looked like a saber-toothed tiger.
Molly Weasley: NOT MY DAUGHTER YOU BITCH! She then proceeds to spam one spell: Stupefy. The kicker here? Stupefy's a spell meant only to stop, but Molly was so pissed off that when she eventually hit Bellatrix with one, it stunned her heart and killed her.
To reinforce just how Mama Bear Mrs Weasley can be, recall fake Moody's speech to his Defence Against the Dark Arts class regarding Avada Kedavera. Specifically the part about how much rage is required to be able to cast it, and actually kill someone.
Mr Weasley also counts. According to Ron, the one time Fred and George tried to get Ron to make an Unbreakable Vow (which actually kills you if you break it) with them, Mr Weasley caught them, and went so ballistic that Fred and George were terrified into never doing it again.
And Hermione Granger. Nerds are scary when they're angry, particularly if they're witches. Her list including punching Malfoy straight in the face, scaring the shit out of the Weasley twins, and putting Rita Skeeter under her thumb.
In Order of the Phoenix, she sets up Professor Umbridge to be abducted by the centaurs in the Forbidden Forest. Assuming that Potterverse centaurs are similar to their mythological counterparts, this would mean that she was most likely raped, which would explain why she's in such a traumatised state afterwards. Since she's enough of a bookworm to know if this was indeed the case, one must ask... What the hell, Hermione?
Despite all that Harry went through he is still a nice guy, just don't call his deceased Mom a bitch or you will end up like his aunt Marge.
And when Harry finds out how horribly the Carrows treated their students, and witnesses one Carrow spit on Professor he cares about, he Batman Grabs a Gun and fires one Cruciatus bullet at each offender.
Hagrid is a Gentle Giant until you insult Albus Dumbledore or threaten someone he cares about. Then he becomes a Nigh Invulnerable half-giant who can concuss ordinary men with a single blow.
Mild-mannered, friendly ProfessorRemus Lupin. At the climax of the third book when he and Sirius confront Peter with the evidence of his betrayal, Sirius asks him casually "Shall we kill him together?" and Remus simply answers "Yes, I think so."
George: "You've never been on the receiving end of one of her Bat-Bogey Hexes, have you?"
Dobby, especially in the second and seventh books.
Professor Sprout is every bit as friendly as Hufflepuff House is renowned for. She is still a fully trained witch with encyclopedic knowledge of many very dangerous plants. Her first act during the Battle of Hogwarts was to have her seventh year students start throwing potted mandrakes out the windows. The scream of a mature mandrake is instantly fatal to anyone who hears it.
Edmond Dantes from The Count of Monte Cristo. Edmond was a guy who had everything going for him, then lost everything thanks to being screwed over by whom he thought were his friends. What ensues is a gigantic Batman Gambit to take revenge on every last one of them and their families.
In the Dresden Files book Summer Knight, the faerie Aurora, the Lady of the Summer Court (which is generally much, much nicer than its counterpart the Winter Court), gets so sick of seeing the suffering caused by the continual war between the two Courts that she kills Summer's human Knight (their emissary to the mortal world), stores his power in a changeling girl, turns said girl into a statue, and plans to sacrifice the girl in order to transfer the power to Winter, tipping the balance of power in Winter's favor and causing the end of the world as we know it.
In the same book, Changeling Fix beats the crap out of the Winter Knight Lloyd Slate with a wrench after he mortally wounds Meryl.
And now Fix is the new Summer Knight, with the powers that come with the office.
Harry Dresden is one of the premier examples of these in the series. He's a cheerfully irreverent geek who cares for his elderly landlady's lawn and has adopted every single stray animal in the series. He's also a deadly wizard, who over the course of the series rises in power from the top half of wizards to the top twenty to the top ten, meaning before considering any of his rolodex of mantles of power, he has the magical punch to go toe to toe with the most ancient, wise, powerful mortals on earth. He does have a notable, if diminishing, lack of subtlety, but when someone is bringing a comet of fire down at you, you're not really concerned about how subtle it was. Tamper with Chicago, mess with the defenseless, threaten his friends, and he goes from one mode to another in a heartbeat. Murphy describes him as a frightening "primeval force of nature", and she's the one watching his back. By the end of Changes, Harry has a killcount up among even the most savage tyrants of human history. By his own hand. The reason: Red Court vampires kidnapped his child, which he only just found out he even had. Doing what he had to do to save his girl resulted in the death of practically the entire Court. A major power in the supernatural world was destroyed that night.
Thomas said it best: “He's Gandalf on crack and an IV of Red Bull, with a big leather coat and a .44 revolver in his pocket.”
On messing with Michael and his family: If they don't get you, Harry will. The line: "Fuego, Pyrofuego! Burn!" comes to mind. As this was the line said by Harry as he blasted a beam of possibly soulfire enhanced flame (the fires of creation), without a focus (which is serious) through a human posessed and wielding the full power of a fallen angel. It counts even more when you realise the last part of the line was an echo of something Superman said, when he completely flipped out at Mongul and used his heat ray vision on him. This makes it even scarier.
Behold Waldo Butters, geeky, cowardly Non-Action Guy. Spends most of Dead Beat panicking and needing to be rescued. But when he's on the ropes, he tackles Quintus Cassius and attacks him with his teeth to save Harry.
Sweet, friendly Perky Goth Molly Carpenter. Nice girl in general, loves her family, has a small crush on Harry that develops into true love, cares so much for her friends that she tries to scare them straight using mind control magic. Also capable of powerful and complex illusions that induce people to kill each other or think that unholy creatures from the Nevernever are after them...
Invoked by name with adult film manager Arturo Genosa.
Damien of Starship's Mage is typically quiet, polite and genuinely concerned about making sure that everyone is treated equitably when he acts as a troubleshooter for the Mage-King. But if you go too far, he won't hesitate to take you down.
Every time she saw the Hand, Amiri started to get nervous. Damien was... young, polite, and, with the Runes of Power carved into his body, an extraordinarily powerful Mage. She also knew, unlike most, that he already had a body count to make serial killers blush.
In the first book of Raymond E. Feist and Janny Wurts's Empire Trilogy, the basically sweet and gentle Mara, who has had the position of ruler thrust upon her, marries a young man who starts abusing her on their wedding night. In response, she manipulates him into a position where he's forced to commit ritual suicide.
Heck, messing with Lady Mara is generally a VERY bad idea. Consider the way she snaps in Mistress of the Empire, when she has her spymaster eradicate an entire order of assassins because they killed her son, another not-yet-born child of hers and very nearly herself.
A special mention must go to Shannon Foraker. Absent-minded tactical officer who consistently forgets to use the approved Revolutionary titles when addressing her superiors, and mostly goes unpunished because she's good at what she does, and she's adorable. Kills 10,000+ mooks in the blink of an eye with a keystroke and the word "Oops."
Commodore Sir Aivars Terekhov always wonder why various bad guys (and gals) of the Galaxy always think that they're more ruthless than him.
None of the humans in the setting hold a candle to bonded treecats, at least on an individual level. Treecats are cute, and make wonderful companions, especially for children. But if you even think about hurting their human, they will turn into flying furry buzzsaws aimed directly at your face.
For the matter of that, it really is not wise to hurt Treecats when a Sphinxian is near. Every Sphinxian will dedicate themselves to making absolutely sure that you are consigned to a level of hell deeper then Dante ever thought of.
The nicest character in the Wheel of Time is Perrin Aybara, a henpecked husband, that's basically his wife's bitch. In one memorable scene after his wife has been kidnapped he chops off an Aiel's hand, orders an Aes Sedai to heal the stump, and then tells the Aiel that unless he talks Perrin will cut off his other hand and his feet, and then dump him into a town, so the Aiel can beg for a living. Then he walks away.
To put this in perspective, remember that the Aiel are a people who live by honor above all else, to the point where some kill themselves over an act of dishonor. And they view beggars as possibly THE least honorable thing to be. Perrin is basically threatening the guy with a Fate Worse Than Death. The Aiel and his companions, who are members of what's known to be the most stubborn tribe out of all the Aiel (which is REALLY saying something), cave almost immediately.
Lanfear finds out too late that despite his strong personal code of honour, if pushed far enough, PerrinWould Hit a Girl.
The Ogier are an entire race of nice guys (on the main continent, at least). The saying 'To anger an Ogier and to pull a mountain over your head' is thought to refer to two impossibilities. Events show that it might have originally read 'To anger an Ogier is to pull a mountain over your head.'
Loial's Crowning Momentof Awesome (so far) is probably when he defends a group of children during a Trolloc attack. People are simple DUMBFOUNDED by his actions. If an Ogier ever tells you that he is "putting a long handle" on his axe...run...run fast.
The Ogier as a group show their mettle in the Last Battle. Their cohort is not so much a military unit as an advancing wall of death.
Rand isn't necessarily a very nice person (being driven slowly insane, having people wanting to control you and having the voice of Lews 'Kinslayer' Therin babbling away in your head would drive most people to more ruthless tendencies), but if you hurt someone he cares about or is related to someone he cares about, you will find out exactly why people fear the Dragon Reborn and he will wipe you from time itself so comprehensively that even the Dark One himself can't save you.
The Betsy the Vampire Queen series gives us Laura, daughter of Satan and one of the nicest people you could meet, since she's trying to be an Anti Anti Christ. Problem is, when she gets mad, she breaks out a sword of hellfire and slaughters everything in the area. Those instincts are a bitch to keep restrained.
More of a "Nice Civilization" than "Nice Person", The Culture, the society in Iain M. Banks's series of novels, makes a point of being morally and ethically spotless, considers it their mission to find and improve the lives of "lesser species," and likes to ensure its denizens live happy and carefree. When you threaten this mission, they will go to war, and you will lose.
Not only that, but the Culture is basically a civilisation of space hippies, whose Hat is "Make love, not war": they are so reluctant to go to war that it takes years-long debate among its 30.000+ billion citizens to makes the Culture go to war. When the Idiran Empire crossed the line in Consider Phlebas, the war that followed caused the destruction of more that 14,000 space colonies, the death of over 850 billion intelligent beings, and the destruction of more than 50 planets and 6 stars: When you encounter space hippies, remember to be polite, courteous, and do not accuse them of being a threat to your way of life: if pissed off, they will blow up your home solar system. They may be softly spoken, but they carry really big sticks.
Stick here being translated as the ability to reduce whatever patch of existence it's being fired at into absolute nothingness. Oh, and every single one of their warships is capable of reducing an entire world to slag, ...on their own... Lampshaded in that one of their spaceships is actually named I said, I've got a big stick (which is supposed to be spoken ''softly''...)
There's the saying, quoted in several books "Do Not Fuck With The Culture." This is proved rather horrifically in Look to Windward.
"You might call them soft, because they're very reluctant to kill, and they might agree with you, but they're soft the way the ocean is soft, and, well, ask any sea captain how harmless and puny the ocean can be."
The Mord Sith in the Sword of Truth series are the kindest, gentlest, and most sensitive girls that can be found. They make the best torturers once they've been broken, because the greatest cruelty comes from the greatest kindness.
Rather a lot of the good guys in the series fit this trope.
In the book The Last Knight, Sir Michael is constantly honest, chivalrous and idealistic, much to his streetwise squire Fisk's disgust. But after Michael has spent a few weeks in a dungeon being force-fed experimental potions, even Fisk notes that he "preferred the crazy Sir Michael to the ruthless one."
Cassie is interesting, because you don't have to get her into an Unstoppable Rage to get bad results. David's fate? That was cold rationalism; she was crying as he got stuck. For another example, the fate of Visser Four's host.
Likewise the Chee - immensely strong androids, and hard-wired pacifists. Except the one time Erek was freed from that part of his programming, and proceeded to wipe out an entire strike force single-handed. It's mentioned at some point that he did more damage in one or two hours than the Animorphs themselves did in months of missions.
It's so bad that Rachel, who has started her transformation into Blood Knight has to suppress the memories.
And the Hork-Bajir are Beware the Nice Ones writ large: an entire race of peaceful, not-very-smart herbivores that are covered in blades so that they could strip bark from trees. The Yeerks happened to think they would make excellent shock troops, and Aldrea, the lone Andalite on their planet, encouraged them to fight back, instigating a very long, bloody war. They lost that one, but the Hork-Bajir who escaped have "Free or dead!" as their motto, and have become very willing to fight and kill to protect what they have, as Dak Hamee sadly observed.
Human-Controllers (Yeerk hosts) generally have public personae falling between "normal but caring human" (Chapman) and "Friend to All Living Things" (William Roger Tennant). The Sharing, "a Boys & Girls Club for everyone" responsible for a great deal of youth work and charity events, is a Yeerk front organization intended to recruit new Controllers.
The book series Murphy's Lore takes place in a supernatural pub. The owner of said establishment is a kindly leprechaun named Padriac Moran, or Paddy for short. Normally, he's wise, gentle, and refuses to kill anything, including undead, because all life is sacred in his eyes. However, if you were to, say, desecrate the memory of his dead wife on the anniversary of her death, which the devil unwisely chose to do, at which point he will have enough alcohol in him to pickle a sperm whale, you will probably find yourself getting crushed as Paddy makes the floor beneath you turn into a mouth and bite you.
Daine is a nice young girl from the mountains with frizzy hair and a good hand with animals. Then tell her that her beloved teacher is murdered. She'll reanimate dinosaur fossils, tear down a palace, specifically destroy tax rolls and imperial records to make the damage last, and get the entire nation's rats to infest the ruins for a year and a day. In the next book, when she finally corners the man responsible, not that Numair actually died, but still: She goes after him buck-ass naked with a badger claw and tears his throat out.
Ashfur from Warrior Cats began literary life as a sweet, shy young apprentice. Then he became the series's most shining example of Break the Cutie, when his best friend is abducted by humans (though only temporarily), his mother is brutally murdered, his father (if you believe the family trees) is killed in battle, he loses the love of his life to the son of the cat that killed his mom, and finally is forced to mentor their kit. He'd always been sweet, gentle, and friendly, but then in Book 5 of the Third Series, he goes insane and tries to kill all three main characters, one of which is his own apprentice. No wonder his fangirls were upset.
The Scolosaurus in The Fantastic Dinosaur Adventure is extremely timid and terrified of humans, but when he is cornered by the Tyrannosaurus, he loses his temper. The results are rather bloody.
In The Night's Dawn Trilogy by Peter F. Hamilton, the always polite and civilised Edenists go to great lengths to avoid killing, but when Al Capone sends a force to conquer a nearby Edenist habitat it gets wiped out. To the man.
David Eddings seems to enjoy this one. Belgarion is a generally nice guy who tries to do the right thing, and if you go after his family or murder some farmers, "the right thing" tends to involve you, his BFS, and a demonstration of why he's allowed to put "Godslayer" on his official letterhead. Polgara has spent most of her life as a doctor and taking care of children, but can give you a matinee of your worst nightmare or turn you into a snake, and she isn't afraid to Shoot the Dog. But for the gold, there's Aphrael and Sephrenia in The Tamuli: upon learning that Zalasta had been plotting to kill Aphrael for several centuries, Aphrael begins planning to eat his heart, and Sephrenia enjoys breaking his spells (which hurts, oh sweet Edaemus it hurts) just a bit too much.
Ender Wiggin isn't "a sweet little kid", he's even sweeter. He doesn't want to hurt anyone. He loves everyone he meets the way they love themselves. And if he determines someone should no longer be able to cause harm, he makes sure that someone will never be a threat, ever. He wasn't called the Xenocide, in the following novels, because he was the Formics' drinking buddy during the first book, after all.
The Dark Elf Trilogy has Drizzt Do'Urden, who at first is depicted as the Wide-Eyed Idealist with a heart of gold. His enemies make the unfortunate mistake of assuming that he's weak and wind up having the living shit being beaten out of him in one of his biggest Unstoppable Rages in the history of dark elves. And he's completely outnumbered and severely injured in most of these battles?
Special mention must be made of Sam, who is a slow, unassumingly loyal every-Hobbit who kills an Eldritch AbominationGiant Spider when it threatens his master. (Technically, he only gravely wounded the Giant Spider, he didn't kill it. Still, he is pretty badass.)
The Ents. Pacifistic keepers of the forests. Once angered, you're in trouble.
Gandalf. Tolkien describes him in the Unfinished Tales as "kindly to the young and simple, yet quick at times to sharp speech and the rebuking of folly" (poor Pippin is usually on the receiving end of his rebukes).
Heralds of Valdemar: Talia of Sensholding, Royal Advisor/Confidant/Babysitter and generally softhearted little Proper Lady sort complete with empathic powers. Sure she has had some self-defense training as a Herald, but one would think that her Companion is a bigger threat than she is, right? Well, those who have pushed her too far would be glad to inform you otherwise... if they stop screaming long enough.
This is true of the nation of Valdemar as a whole. Their national motto is "There is No One True Way"; they were founded by refugees from despotism, and have never engaged in a war of aggression or expansion—their boundries have been expanded only through colonizing uninhabited wilderness or through less developed or weaker states voluntarily joining themselves to Valdemar. This has led to some more aggressive and imperialistic countries thinking they are pushovers; this is not so.
Kaitlynn in Privilege seems to be a Nice Girl, to the point where Ariana swears revenge on the girl who framed her...but when she fails to get her hands on the girl's inheritance, Kaitlynn snaps and reveals her true form: she was guilty after all, and is in fact quite the vicious little cold-blooded killer. She then becomes the series antagonist.
Mendoza from the Company novels, left to her own devices, is a quiet botanist. Give her a love interest, and she turns spy. Kill him, and suddenly she starts throwing human heads around.
The heroes of Redwall are cute fuzzy little woodland animals, who live happily in an Abbey devoted to upholding peace. And if you wrong them, they will fuck you up.
Two words: Badger Lords. Wise and caring leaders of Salamandastron. Get into a fight with them and the bloodrage takes over. A fully armored Badger Lord in a full-on bloodrage is capable of taking on a small army by himself.
Or herself. The Badger Mothers of Redwall are gentle and loving, typically somewhat older badgers who typically watch after the young children in the Abbey. But if you threaten anyone, especially those children... well, you're going to find out pretty quickly that sweet older female badgers are just as capable of murderous bloodrage as the Badger Lords. Special points go to Cregga Rose Eyes, who used to be a Badger Lord—well, Lady, but she ruled Salamandastron, and was one of the most powerful warriors in the series, even after she went blind and took up residence in the Abbey. She's the one who offsRaventail and (with Ellayo's help) Ascrod in Marlfox.
While Morrolan of Dragaera is portrayed in the main series as a Lawful Neutral (or possiblyLawful Evil) Jerk Ass who pets the dog frequently, his presentation in the prequel novels is as this. The narration talks about him being a rather amiable guy during his period of Oblivious Adoption, and had yet to lose his temper, since everyone around him was wise enough not to do anything to elicit an angry Morrolan. When followers of a Religion of Evil kill some of his friends and torch part of his village, Morrolan's revenge consists of slaughtering three villages of these worshipers, man woman and child, and then killing their god.
Nathan Slaughter of the 1837 novel Nick of the Woods. A Quaker and often made fun of by the townsfolk where he lives for his pacifist ways, turns out to be the Jibbenainosay that's completely terrifying everyone in the area by his massacre of the surrounding Indian population.
Sadrao from Black Dogs is probably the kindest, politest, most caring and definitely the most loyal character in the whole series. Don't ever threaten any of his wards or former wards, though... In the act of defending and protecting Lyra, he literally bites off a bandits face, tears apart an entire church and is completely unapproachable by anyone. Even the person he's trying to protect has to take caution not to get caught in his berserker rage.
Karl Sadeghi, from the Doctor WhoEighth Doctor Adventures book The Year of Intelligent Tigers, is a shy male Meganekko, who occasionally stutters. He's a musician and a generally sweet guy, and although the Doctor knows how to annoy him (because they're so close, and the Doctor really is very annoying), it seems his record for getting angry is a whopping page and a half. Then he gets kidnapped and mistreated by talking tigers. So he intentionally opens up a dam to drown a whole bunch of the poor, sapient tigers. To be fair, the tigers killed several people, but not all the ones he killed were dangerous.
Yumiko Shirasagi of Digital Devil Story is very sweet and mischievous, a fun girl, really. She's also the reincarnation of the goddess Izanami, and she teaches Loki a thing or two about the efficacy of fire.
In War of the Dreaming, Titania is one of the few characters unreservedly on the side of humans, and who respects them for their own merits, rather than seeing them as pawns or Puny Earthlings. She's behind many of the historical human victories over the Fae (even though some of those victories hurt her as well). She's also the Queen of Nemi James Fraser was talking about in The Golden Bough. The one annual kings were sacrificed to.
In the Star Wars Expanded Universe, Luke Skywalker's characterization varies pretty significantly Depending on the Writer. But his characterization in Luke Skywalker and the Shadows of Mindor is very much this. When he has any choice at all, he resolves things peacefully. He will forgive anything, if you try to make up for what you've done. He gives you a lot of chances to be reasonable, and will wholeheartedly regret the loss of life if you don't take them. After Luke lets himself get captured, he asks too many questions and a stormtrooper clubs him with a blaster rifle, telling him to be quiet. Luke says "Please don't hit me" and is smacked again while the stormtrooper says "Didn't you hear me?" Luke says he did, but didn't see any particular reason to obey. The stormtrooper tries to hit him a third time, and Luke catches the blaster rifle and shatters it. Another stormtrooper tries to shoot him; Luke catches the blaster bolts.
"Please don't shoot me, either." He turned the palm upward in a friendly shrug and let the astonished troopers stare at the only effect of the Force-blunted blasterfire: a faint curl of steam that trailed upward from his unmarked palm. "Let's try to end the day with nobody else dying, shall we?"
In Princess of the Midnight Ball, we get 12 princess, all very nice( although the eldest and love interest/ main character(sometimes) is snarky at time.) but I'm not talking about Rose. no, I'm talking about her sister, Lily. Lily is the second oldest- never complains about her lot in life, never gets snappy, very, very sweet- never violent in the least. And then she and her sisters get taken to the World Under Stone, with arranged marriages ( with half demons) in mind. during Rose's one true love's rescue attempt, Lily gets her hands on a gun. turns out her own one true love taught her how to shoot. things don't end well for the attackers.
Galen himself( the real main character) counts as well- he just wanted to be done with war, and is one of the nicest guys ever- even giving up his last bit of food to an old beggar. then Rose goes missing, and he's ready, armed with magic, a gun, and pure Bad Ass-ery.
Daphne of Sisters Grimm is a a sweet little 7 year old, who loves everybody( even the big bad wolf.) she doesn't have an evil or violent bone in her body. but if you mess with your family, she will try her darndest to end you, and she's not the keeper of a ton of magical items for no reason. she causes a tornado. 'nuff said.
Ryo, the namesake of The Longing of Shiina Ryo, wishes to inform you that it is unwise to ignore her. She will use an ASCII weapon of mass destruction if you do. And that's just her warm up. Gravity is her friend, not yours.
The Mule from Foundation and Empire
Also, Hari Seldon. This calm, rational professor of Mathematics will beat you up using Heliconian Twisting, in front of hundreds of students, if he doesn't like what you have to say.
Percy Jackson's mother Sally is the ideal mom. She always makes him feel good, and both of them find it impossible to stay angry at the other for long. But just about anyone would snap from year after being married to an abusive asshole like Smelly Gabe. And when she gets her hands on Medusa's head...well, you can pretty much guess what happens. She goes back to her normal self after this, though. But in Book 5, she (and her second husband, Paul Blofis) fight ferociously to defend New York from Kronos and his armies.
And then there's Grover. He's a clumsy, Adorkable satyr most of the time...but when he needs to be, he can be incredibly badass, especially after he gets the gift of panic.
Annabeth's dad, too. One moment, he's an eccentric bookworm who wears an aviator's hat around the house; the next, he's flying a Sopwith Camel into battle and spraying celestial-bronze bullets while wearing the same aviator's hat.
Percy himself is a pretty nice guy in a similar vein to Harry Potter, yet he is capable of beating up gods and taking down the entire Roman army.
Mild-mannered science fiction author Peter Frigate of To Your Scattered Bodies Go by Philip José Farmer is not afraid to fight, he's afraid to unleash the rage within. People die when that happens.
In Wearing the Cape, Hope Corrigan, who at the age of 18 stands less than 5 feet tall and is self-described as an "underdeveloped teenage Tinkerbell", is one of the strongest superheroes on the planet (in the top 10%, anyway). Also, though she spends a good deal of time worrying about accidentally hurting anyone, she opens an alarming can of Whupass at the end of the story.
In Enid Blyton's Famous Five books Anne is a young lady in training. Occasionally she ulitizes this trope.
Likewise, Mary-Lou from Malory Towers, although for her it takes the form of conquering (usually permanently) fears which previously would have paralysed her. Anything for a friend, especially for Darrell Rivers.
In a similar vein to Enid Blyton, Elinor M. Brent-Dyer's Chalet School series has Frieda Mensch and her cousin Marie von Eschenau, who make up half of Joey's Quartette and are both kind, gentle, sensible Tirolean girls, in contrast to the more Hot-Blooded Joey and Simone. However, Frieda's sharp tongue keeps juniors in line, and Thekla von Stift finds out the hard way that making Marie angry is a bad idea, after she insults Marie's family, and Marie loses it and shakes her.
Nick Chopper (the Tin Man) in Baum's Oz novels. He is, hands-down, the sweetest, kindest guy you will ever encounter. He cried himself rusted after accidentally stepping on a bug because he regretted taking innocent life. When it comes to creatures threatening innocent lives, or those of his True Companions? The axe comes out and heads start rolling. Baum even lampshades it in the second book by stating that Nick "fights like a Roman Gladiator."
Ibram Gaunt cam be considered an example of this. By Imperium standards, he's pretty reasonable. Get someone killed through incompetence or stupidity, however, and he will not hesitate to make an example of you.
"Men have been shot for that kind of carelessness - some by me."
At the beginning of The Tomorrow Series, the main characters are a bunch of nice, normal, reasonably-harmless Australian small-town and farm/ranch kids. When they find their country's been invaded and their families have either been killed or rounded up and imprisoned...that's their Let's Get Dangerous moment, and they eventually become guerrillas with an international reputation, and tops on the enemy's "better dead" list.
In Mario and the Magician by T. Mann, the magician Cippola uses his powers on a nice sweet waiter Mario. He forces Mario to reveal whom he is in love with, and then, makes him believe that he is that girl and that Mario should kiss "her" - all this during the show with hundreds people watching. Then Mario is snapped out of his trance and realises he just kissed Cippola instead of his girl in front of all those people (who are amused by his ordeal) and is basically humiliated into the ground. Sounds sad? Well, directly after that, Mario shoots Cippola dead. End of story.
Stephen King and Peter Straub's collaborative novel The Talisman gives us Wolf, a friendly and sweet (if a bit slow) young shepherd of the Territories who immediately takes to twelve-year-old Jack and adopts him as his new "herd". He's also a werewolf. And god help you if you decide to hurtJack.
Patrick Rothfuss even has a book named after it. In The Wise Man's Fear it is stated that "There are three things all wise men fear: the sea in storm, a night with no moon, and the anger of a gentle man."
Trapped on Draconica: King Alister is a good man with great patience but don't push him. Official art shows him to be very scary when administering justice.
The Kane Chronicles in a similar vein to Percy Jackson has many nice characters who, when fully pissed are terrifying. Carter Kane and Amos Kane being examples
In The Adventurer and The Wanderer by Mika Waltari, Antti is a Gentle Giant and usually very friendly and seems like a quite harmless person. But he's surprisingly cunning in addition to his incredible body strength, and if you fail to take heed of his gentle warnings you may find yourself in a bit of a pickle. By which I mean dead.
Nice, neglected side-hero Edilio Escobar finally has a go at the ignorant main characters about how little he's appreciated in FEAR.
In the Spin-off series The Hardy Boys Casefiles, they finally started to split up the brothers' personalities. Joe became a very easygoing, joking, flirty, friendly 17-year old. However, do not mention the fact that his girlfriend Iola was blown up in a car bomb by terrorists (which was the plot of the first book, Dead on Target.) Even Frank had to learn this the hard way.
Kendra Sorenson from Fablehaven. A sweet teenage girl who reads books to children. Hates to touch weapons. Not all that brave. Beheaded the King of Demons, a virtual god, when he attacked her boyfriend. Not to mention she's a great Action Survivor.
Michael Hosea of Redeeming Love is a polite, easygoing gentleman who has his opinions but isn't the type to get up in anyone’s face about them…until he catches you hitting Angel and/or naked on top of Angel, in which case you’d best hope he’s just too blinded by rage to hit you straight.
“Does anyone else want to get between me and my wife?
Phenix from Of Fear and Faith. He's very sweet and protective of his friends, and a total pushover (especially with women) and he hates to fight. That said, that doesn't mean he can't fight, and he really doesn'ttake kindly to people threatening his friends.
Towards the end of the Gemma Doyle trilogy, Gemma's brother Tom has been kidnapped by the Rakshana, in order to force Gemma to hand over magic powers. This is after a long book of being harassed, provoked, threatened, and blackmailed by the Rakshana, and this is the last straw. Gemma tells them, in no uncertain terms, that so far, she has played nice because her brother is still alive. If he dies, there would be nothing stopping her from killing them. Initially, the Rakshana scoff... not realizing that Gemma is very good at using her Master of Illusion magic. Cue Gemma curb-stomping the entire organization by herself.
Flight To The Lonesome Place: When Anna Maria Rosalita is mad, watch out. She'll take being held prisoner and starved, but threaten her friends...
The protagonists of LE Modesitt JR's Saga of Recluce novels are generally fairly nice, reasonable folks - your woodcarvers, your smiths, your aliens dropped onto a hostile world of magic who just want to be left alone. Then they get pushed a little too far, and suddenly your nice, beautiful city of white melts like a tapioca sculpture in the oven. Or half of your island slips into the sea.
Fellow Man, written in Norway in 1929 has the protagonist Ragnhild, a housewife and mother seemingly not capable of thinking a bad thought, and known to be kind to everyone. When the antagonist of the story, the Magnificent Bastard Didrik pushes her too far, after she has tried to redeem him a number of times, she conveniently kills him with an axe. Being the benevolent heroine, she immediately goes to face the consequences and gives herself up.
In Robert A. Heinlein's Have Space Suit – Will Travel, the Mother Thing is gentle, soft spoken and eternally pleasant, with a small, frail looking body and enormous lemur like eyes. She also is fully capable of building a pair of bombs to destroy an alien base under her captors' noses and kill all of its personnel to guarantee her, Kip and Peewee's escape.
In World War Z, a quiet Palestinian father goes Papa Wolf on his son in order get him to go with the rest of the family to the Israeli quarantine zone, instead of blowing his life away by becoming a suicide bomber.
"He knew that fear was the only weapon he had left to save my life—and if I didn’t fear the threat of the plague, then dammit, I was going to fear him!"
A suburban housewife allegedly tearing a zombie's head off to protect her children, and an old nun described as 5 foot, 100lbs defending her Sunday school class from a horde with an iron candlestick taller than she was (who later joins the Army!).
Laughing Winds has Annika. She is normally a sweet, polite, and gentle person. She is also trapped in a death camp. One night she sees a guard pulling a childs' remains out of furnace the same night her little brother disappears. The next day the same guard makes the mistake of confronting her while she is working on the assembly line and holding a heated saw.....it doesn't end well for him.
Angel, who can be a bit mean and abrasive but is generally a sweetheart who gives the impression of a man who wouldn't hurt a fly, is not one to be trifled with. Being a woman will not stop him killing you, even when two characters with substantially higher body counts refuse. Hurt him personally, and he will not rest until you are dead. Get involved in any way with child pornography or prostitution? You might as well get started on digging your own grave right now, 'cause he's gonna be after you.
Then there's Rachel, Charlie's girlfriend who is cast firmly as The Chick for most of the series. But she's smart, and quick, and don't bother even trying to lay a hand on her, because it will not end well. especially if she's pregnant.
The main theme of Rudyard Kipling's poem "Et Dona Ferente" is "Do not piss off an Englishman." Because these stuffy, well-mannered, almost-comically polite guys who'd rather do their fighting with worlds than swords and guns? Well, they can afford to be this way for a reason.
Peeta Mellark is The Heart of The Hunger Games series, a kind and gentle person who prefers diplomacy to violence and who likes to paint and to bake. He is also skilled with a knife and a spear, has a body count of at least three people in the books (four counting Foxface and possibly one or two at the Cornucopia, although hist first known kill was a Mercy Kill), is a wrestler with a great deal of strength and when angry he is definitely deadly. Which does not bode well for Katniss after he's been subjected to Mind Rape designed to make him fear her and want her dead.
Odd Thomas is probably one of the nicest heroes in contemporary literature; unfailingly polite, respectful of everyone, great with kids, and generally tries to avoid violence. He also can see the spirits of the lingering dead, is an unshakeable Determinator, and if he finds out that you've done evil or are planning some, he will bring you down as sure as the turn of the world.
The Bad Unicorn Trilogy: Moki of all people gets very angry in the second book when he learns that Loki tricked him. In the third book, he again proves to be just as capable a fighter as the other heroes.
The Secret Garden: Martha gives off this vibe. Mary once considers slapping her like she did to her servants in India, but thinks better of it because Martha "seemed like she might slap back".
Kulingile from Temeraire is much more easy-going than most other dragons. He's also the second biggest dragon in the series (and the biggest that can fly), has oversized talons, a spiked tail, and repeatedly turns crowds of humans that threaten his captain into Ludicrous Gibs.
In the Literature/Cut and Run and Sidewinder series, Kelly Abbott is the smallest and sweetest member of Team Sidewinder and is basically the baby of the team. He is also the one that every other member of Sidewinder says you don't want to piss off.
The Hollows has so many examples. Rachel is nice enough, but if pushed far enough she'll use any method availableto protect her own. Ivy, her roommate, has a vampire's instincts to protect the weak and sick and volunteers with children at the hospital, but she was raised by Piscarey and is extremely protective of Rachel. Jenks is the nicest pixie you'll ever meet, and he'll labotimize you if you ever harm his family. Ceri is as nice and unassuming as you'll get, and is capable of curbstomping a man who curbstomped Rachel. Suffice to say, Good Is Not Soft in this series.
Christine Rhoades is seen as angelic by a lot of the Suburbians in Spectral Shadows. When Dr. Reinhart pushes her over the edge the narration mentions that none of them ever imagined Christine being able to use her magic for anything other than healing, to say nothing of them never expecting to feel anything but good vibes from her.