This is the entire premise behind John Grisham's A Time to Kill. After a brutal first chapter detailing the rape of his 10-year-old daughter by a couple of rednecks, Carl Lee Hailey (played by none other than Samuel L. Jackson in The Film of the Book) goes berserk on the two and opens fire on them with an assault rifle (even though they were already on trial), catching a court deputy in the process. The deputy forgives him, as does the jury when they acquit him of murder charges by reason of "temporary insanity."
Woe betide whoever dares to abduct Popsy's grandson.
The Jungle Book: Akela, who acts as a father for Mowgli despite not necessarily being his adoptive father, and is a literal wolf. Baloo and Bagheera qualify, too (despite being a bear and a black panther, respectively). Akela stood up for him when he was brought to the pack as an infant (after Raksha saved him from Shere Khan), Bagheera bought his life and protected him ever since, and Baloo taught him the ways of the Jungle - and when he's kidnapped by the monkeys, they join with Kaa to make it a day and a night the poo-flinging rabble will not live to regret...
Sergeant Jackrum from the earlier book Monstrous Regiment is an example, being A Father to His Men who regularly kills, injures, or otherwise incapacitates anyone stupid enough to threaten one of his Little Lads. Until we find out that "he" is actually a she who's been masquerading as a male soldier for longer than she can remember, technically making Jackrum a Mama Bear.
Subverted in Wyrd Sisters, in which the late King Verence tries to charge ferociously to the rescue of his son, but is balked because he's now a ghost and can't leave the castle.
Mustrum Ridcully is, in spite of all their failings, strongly loyal and protective of his faculty. For example, he is willing to summon DEATH to find Rincewind's whereabouts, and orchestrate a ritual to teleport him half-way across the world to get him home. Also, his reaction when the Librarian appears to have been poisoned is one for the books:
"[I]f anyone has poisoned our Librarian, then, although I am not, by nature, a vindictive man, I will see to it that this university hunts down the poisoner by every thaumic, mystic and occult means available and makes the rest of their life not only as horrible as they can imagine it, but as horrible as I can imagine it. And you can depend on it, gentlemen, that I have already started work on it."
Hector Malot's Sans Famille. The travelling musician Vitalis practically purchased lead character Remi Barberin as his apprentice, but he genuinely cared for the boy and became his mentor and example. His "Papa Wolf" side shows more strongly when he discovers that the old man whom he was going to ask to look out for Remi in the winter actually abuses his protegees and forces them to steal for him, and later when he protects Remi from dying in a snowstorm... in a Heroic Sacrifice. And he was also hinted to be one in his first apparition, when he "buys" Remi... after witnessing how horribly his abusive stepfather Jerome treats him, therefore choosing to "purchase" Remi half to have an apprentice and half to protect him.
Individual names are not given but in Harry Turtledove's Worldwar Tetralogy, the Alien Fleetlord is amazed at reports of suicidal Tosevite (read: Human) attacks by both genders on his forces. Its stated that the few humans that actually survive indicate their actions are because of harm done to a Mate or Hatchling by his forces
Dr. Radcliffe Emerson, the Egyptologist-detective husband of Amelia Peabody, is always short-tempered and becomes absolutely volcanic at any threat to his family. Since he is regularly described by his narrator-wife as "Herculean" in build, the results are impressive. For that matter, his son Ramses inherits this trait. Guess what? Their wives are definite Mama Bears; it's a close-knit family.
Honor Harrington: Anton. Zilwicki. Messing with his kids is the last mistake entire secret societies ever make. The entire planet Mesa and its Ancient Conspiracy may yet fall through the chain of events set off the first time they tangled with him.
Not to mention that we have yet to see his reaction to the latest atempt by Mesa to kill one of his daughters. The foreshadowing in At All Cost might give some clues.
And don't forget Anton's best buddy Victor Cachat and Victor's mentor Kevin Usher, who got off their asses and did something about the corrupt Havenite ambassador, because of Zilwicki's daughter kidnapping. Honor herself has her moments -- the surest way to get her to kill you, is to mess with somebody in her care. In fact the whole series is full of Papa Wolf and Mama Bear moments, from the lowly Aubrey Wanderman to the Queen herself, to the whole nation of Grayson which are all, 2 billion of them, a bunch of Papa Wolves.
Also don't forget Nimitz. He may be a Ridiculously Cute Critter most of the time, charming people's socks off to glom some more celery, but if anyone harboring murderous intent gets within spitting distance of Honor, he'll instantly transform into a six-legged, self-propelled chainsaw with absolutely no mercy. (He's also probably older than Honor's father, so he qualifies under the "Papa" portion of the trope as well.)
Not to mention that about halfway through the series he finds a mate and they promptly produce a litter of four treekittens.
In Perry Moore's Hero, Hal Creed, a 100% normal (granted of the badass variety) Human, beats the shit out of a Superman expy for threatening his son.
Burrich in both the Farseer and Tawny Man trilogies. Just how awesome can a grumpy old man be? Trek across a glacier and kill a deranged stone dragon for the adopted son who let you think he was dead for 15 years, that's how awesome.
Raptor Red's consort pulls a Papa Wolf to save one of Raptor Red's nieces from an acrocanthosaur. He has mixed feelings about doing so: he gets several cracked ribs, the chick isn't related to him, and Raptor Red didn't even see his heroic actions. It does, at least, mend his relations with Raptor Red's sister for a time.
Most David Eddings characters fall into this at some point: if you go after their wives, kids, fiancees, or friends, they begin throwing around phrases like "boiling oil," "wring him out until his hair bleeds," and "kill him just a little bit." Then they catch you. Then you discover this was them being nice.
This trope applies especially to Belgarath. He not only has a few Wolf-themed nicknames, but also likes to turn into a wolf whenever he has the chance, and is even married to one. It works especially well because most of the time he prefers to give off the impression of a lazy drunken hobo. Barak on the other hand is scary enough in his normal form, but whenever Garion's life is threatened, he goes into a berserker rage and turns into a bear.
Belgarath certainly qualifies, particularly given the following exchange after Chamdar/Asharak the Murgo has killed - by burning them alive inside a stone house - Geran and Ildera, the parents of Garion and both of whom were much loved by both Belgarath and his daughter Polgara. Who are also two, it must be said, of the most powerful beings currently walking the earth:
Khonar (about Asharak): Our agent reported that he seemed a little nervous about something.
Belgarath:I can imagine. He's done something that offended me. I want to talk with him about it, and he'd rather avoid that conversation — since it's very likely to involve my hanging his entrails on a fence someplace.
When his turncoat brother kills Durnik, the 'son in law' figure, Belgarath Takes A Level In Badass and commits Zedar to the earth; literally. When he returns from the surface to the point that the book describes him as NOT what he was throughout the entire Belgariad, but "Belgarath the Sorcerer in all his fury."
Polgara says herself that Asharak likely crawled under a rock someplace deep and dark and very well-hidden to hide, solely to escape from the wrath of her vengeful father. A man who, it must be said, is considered by Asharak and his people to be the equivalent of the Devil. Skilled Angarak sorcerers are terrified of being within fifty miles of facing him, and she has also admitted that his power is one of the only things in the world that has held the Angaraks back from just overrunning the west with sheer numbers. Not the sort of Papa Wolf you want chasing after you with a single-minded purpose so strong that he can literally ignore rest, food, and the other necessities of "mere mortals" for weeks or even months at a time.
This applies to Garionas well, but only in the sequel to The Belgariad, The Mallorean, in which the entire plot revolves around Garion turning the world over to get his son back from an evil sorceress, leading to a very satisfactory pay off when he finally catches up with her
Eddings seems quite fond of these graphic descriptions. As pointed out by Xanetia in the Tamuli, after Zalasta, former advisor and supposed ally, reveals that he has been working for the Big Bad Cyrgon since before the start of the series itself. And he has been deceiving and betraying Sephrenia, Team Mom and beloved by all the characters, for that same length of time, all in the hopes of killing the goddess she worships — also Sephrenia's younger sister via reincarnation - and possessing her out of lust. Boiling oil, hooks (nice long ones with sharp barbs on them) and their like are mentioned by several of the main characters. The quite civilised and cultured Sarabian is somewhat unnerved, asking them all if they have to be so graphic. He is told in no uncertain terms:
Kalten: Zalasta hurt Sephrenia, your Majesty. There are twenty-five thousand Pandion Knights — and quite a few knights from the other orders as well — who are going to take that very personally. Zalasta can pull mountain ranges over his head to try to hide, but we'll still find him. The Church Knights aren't really very civilised, and when somebody hurts those we love, it brings out the worst in us. Sparhawk: Well said.
Oh, and that goddess? She also happens to be Sparhawk's daughter (via another reincarnation as a favor). She's immeasurably more powerful than him (without Bhelliom, that is), but he takes threats sent her direction very... personally.
In The Dresden Files, although Harry is grown, and was his apprentice for only two years, Ebenezar McCoy is capable of this on occasion. In Summer Knight, he is so indignant that Harry is to carry out Mab's request without even knowing it that it takes Harry two tries to get through that, yes, he does know it. And he dropped a Russian satellite on the headquarters of a vampire who had threatened and fought with Harry.
Eb's reaction is explained in the novel Changes: Ebenezar is Harry's maternal grandfather.
When confronted by Lara Raith on Demonreach, Lara makes a few veiled threats towards Harry. Ebenezer tells her she can try, if she doesn't mind her family having nothing except a pair of $500 shoes to bury.
What about Michael? He's a sword-wielding knight of God. He has a daughter who is about to be executed by the White Council Elders, who are powerful enough that even if you manage to kill just one of them, it would release a death curse which would be the magical equivalent of head butting the trigger of a 10-mega-ton nuclear warhead. He is exhausted and heavily wounded from battle. Yet, without the slightest hesitation, he immediately prepares to take them all on at once, even knowing that afterward, should he somehow miraculously survive, he would forever more be on the run from every single white court wizard in the entire world.
That was Harry. Michael, while he would certainly do that, simply had faith that God would help him out. Which he did, by zombie-dinosaur riding spell-slinging wise-cracking Honor Before Reason proxy.
While we're talking about Michael, though... nine words. "That son of a bitch hurt my little girl."
Harry also manifests this attitude toward Ivy.
In Changes, the Red Court of vampires takes his daughter with the intent of sacrificing her to fuel a massive curse that will kill her entire bloodline. He responds by joining forces with Mab and becoming her Knight, sacrificing two people on altars, and genociding the entire freaking Red Court.Don't fuck with Harry Dresden's family.
He actually stated that if the world came between him and his daughter, it could burn to death and they would sit roasting marshmallows upon its roaring flames.
And just to be clear, he picked Mab because she was the least evil option, but he was perfectly willing to call up the Blackened Denarius and make a literalDeal with the Devil if he needed to. And if that didn't work, he was ready to invoke the Darkhallow, which would kill everyone in Chicago and allow him to eat their souls.
Harry also serves as a surrogate Papa Wolf to the Carpenter family when Michael is otherwise occupied, as seen in the short story "The Warrior."
Not to mention in Proven Guilty, when he teamed up with Mama Bear Charity to storm the freaking Winter Court in order to save Molly.
Hell, he spends most of that book playing Papa Wolf to Molly, as her boyfriend would attest.
An odd example from the series is "Gentleman" Johnny Marcone, the local Mafia boss who is essentially a Papa Wolf to every child in Chicago. If Marcone catches you doing anything to hurt children in his city, he will personally execute you. Youdon'twant that.
In Danny, the Champion of the World, it's revealed that Danny's father's main reason for disliking Hazell is because he threatened Danny. Later on, when Danny gets caned by his teacher, his father threatens to go down to the school and beat the teacher.
Let's not forget Dallas' reaction to Finding out Johnny was dying from his burns. Mind you, by this point the reader already knows how dangerous Dallas can be, but seeing him threaten to put the doctor in the emergency room for barring him access to Johnny's hospital room seems to be a bit of a case of Disproportionate Retribution.
A slightly twisted variant occurs in Dexter By Design: Dex, of course, is already a Serial Killer masquerading as Just a Nice Guy, but it wasn't until relatively recently that he decided that he had feelings of love-ish for his stepfamily and foster sister (or, you know, anyone). So, when a rival slasher decides to mess with Domestic Daddy Dexter by stabbing Debbie and trying to kidnap his stepkids, out comes Deadly Defensive Dexter.
Adam Hauptman, from the Mercy Thompson series. Bonus points for being a literal papa werewolf; mess with his daughter Jesse and you. Will. Die.
The above also applies to Mercy. To make it worse, Adam runs a private security firm, so when he got worried about Mercy's safety, he installed an expensive security system in her house without asking her permission.
Waylander the Slayer from the Waylander series of books by David Gemmell is a rather evil version of this. Having returned home from the war to find his wife and child killed, he spends the rest of his life and wealth hunting down the eight men responsible and killing them in ways that'd make even the most villainous of villains shriek.
In Charlotte's Web the Gander threatens Templeton the Rat with serious bodily harm if he even thinks about bothering one of his goslings.
One of the recurring themes in The Catcher in the Rye was Holden Caulfield's desire to protect children from the bad things in the world.
Thrackan: "General Antilles, acting as Chief of State and Minister of War for Corellia, I hereby order you to communicate with your daughter Syal and do your genuine best to persuade her to follow whatever course of action I recommend to her. Is that clear enough?" Wedge: "Absolutely." Thrackan: "And?" Wedge: "Go to hell." Thrackan: "Antilles, you've refused a direct order given during a military crisis, and I have it on record. Should I choose to, I can have security agents haul you away right now. I can conduct your trial within the hour and have you executed by morning." Wedge: "Of course you can. You could also have me assassinated in a time of peace for having nicer hair than you. If I worried about that sort of thing, I'd never get any sleep."
Woe to you if you mess with anyone in Mandalorian Kal Skirata's biological or adopted family.
Speaking of Mandos, Boba Fett in Bloodlines is this. So is Han. They team up.
Speaking of Boba Fett, he was never a very good father (or husband), but he did his best to get close to his granddaughter, Mirta Gev. When he learns that a young Mandalorian is planning to marry Mirta, he gives his assent, but warns "Break her heart and I'll break your legs."
This is part of the reason why Jacen Solo turned to the Dark Side and became the Sith Lord Darth Caedus, in addition to the Well-Intentioned Extremist trope: When he saw into the Pool of Knowledge and saw a man clad in Dark Armor (later revealed to be Darth Krayt) sitting on the Throne of Balance and seeing Allana, his daughter, standing by his side, he decided to become a Sith Lord in order to prevent that future from occurring, or at the very least prevent the part of the future where Allana is evidentially serving Krayt as his right-hand servant.
In Galaxy of Fear, Hoole is... not a great uncle to Tash and Zak. He's pretty distant and gets irritable when they ask questions. However, he does take their welfare seriously and will readily threaten anyone who seems like a danger to them. Hoole is also a shapeshifter, and his favorite "strong form" is that of a Wookiee.
Booster Terrik is a Jerkass in general (especially to Corran Horn), but he cares very deeply for his daughter Mirax and his adopted son Wedge Antilles. He'll do what he can to help them...and woe to you if you threaten, hurt, or kidnap either of them. What's more, he's got a Star Destroyer, which may or may not be fully armed and dangerous...and you probably don't want to take the chance that it is.
Howl is this after his son Morgan was threatened. He punched the guy twice. Not to mention his wife, Sophie is a Mama Bear also. In other words, don't mess with Morgan ever.
Sadrao from Ursula Vernon's Black Dogs is not the protagonist, Lyra's, biological father, but he's a more than competent replacement after her real father is massacred along with the rest of her house. Sadrao's extremely Badass and is very protective of her, even going into a berserker-like rage when she's physically threatened.
The Acts of Caine: Caine. Even if you're a god, fucking with Faith will get your ass beat.
Harry Potter: Dumbledore. Harm one of his students, and he'll return the favor.
This is beautifully demonstrated when Dolores Umbridge shakes Marietta Edgecombe violently in an effort to make her spit out enough info to get Harry expelled. Dumbledore magically pushes her away, jumping suddenly from calm and polite to highly angry. "I cannot allow you to manhandle my students, Dolores."
For context, this is right in the middle of Umbridge making her move — because Dumbledore has done nothing worse than tell the truth to the media, she is in the middle of a plot to not only strip him of his various honors, oust him from his job, and take over his beloved school, but also lock him up in prison, an idiotic move that could quite literally get them all killed. Seeing Umbridge get physical with one of his students is the first and only thing on that list that actually makes Dumbledore angry.
This is also demonstrated when Barty Crouch, Jr. attempts to kill Harry after the Triwizard Tournament. Dumbledore doesn't take it very well.
Happens even earlier in the third book. Hermione tells Harry that seeing Dumbledore flip out after the Dementors nearly killed him was really scary. It was the first time she had ever seen him so angry. It probably didn't help that Dumbledore already hated Dementors before the incident.
Papa Wolves are fairly prevalent in this series: Sirius Black does not like seeing Harry hurt, and neither does Remus Lupin.
Mess with Draco Malfoy when he's at school, and the next person you'll have to deal with is his favourite teacher and godfather-of-sorts Severus Snape, or worse still, Lucius Malfoy, his actual dad, with the power of the school governors, as well as the Ministry of Magic behind him (and not to mention, Lucius's love for his family is pretty much hisonlygood trait).
Arthur Weasley, while usually overshadowed by his Mama Bear wife, in Deathly Hallows, threatened Kingsley Shacklebolt (trained Auror, later takes on freakin' Voldemort) to his face when he heard that one of his sons had been badly injured and Kingsley was trying to question him. Earlier in the series, Ron mentions that the only time he ever saw his dad get really angry was when Fred and George tried to make Ron perform an Unbreakable Vow, a ritual that kills the oathbreaker, as a prank.
Arthur is particularly worth noting because Word of God states that he was supposed to die. Rowling intended for him to not survive beyond the fifth book. She ultimately chose to let him live because he's such a good and loving father.
And Harry's Uncle Vernon, who - though he often falls into the categories of Abusive Parents (toward Harry, of course), MuggleandBumbling Dad - is very protective of his own wife and son and is even willing to shield them from Hagrid. Note that because of the strict gun laws in the United Kingdom, he would almost certainly of obtained the gun illegally.
James Potter as well. It may not have worked, but he was willing to risk certain death against Voldemort if it gave Lily and Harry time to run. He would also do anything to help his friends in his school days, even if he was a Jerk Jock to everyone else at the time.
Twilight: Jacob Black is a rather literal example (boy turns into a wolf) when it comes to Renesmee Cullen, the girl he's imprinted upon. Actually, this would apply to any wolf who has imprinted on a child.
Don Pendleton's The Executioner series has Mack Bolan wipe out major crime families with dozens of thugs at their disposal after most of his family is killed due to the Mafia. When his girl-friend and younger brother are kidnapped by another crime family to try to get to him, he goes absolutely coldly berserk, terrifying even his friends and allies who have seen him in action many times.
Matthew Reilly's Huntsman series. The adopted daughter of Jack West Jr. is threatened many times by many powerful people over the course of the books. Many people have died very graphic, painful deaths.
"Damn your ship." Helton's voice grated. "It was you. You were aboard at that time. Outside of the range of the Mentality, beyond the reach of any resurrection circuit."
Catherine Webb's Horatio Lyle. He is not related to Tess or Thomas by blood, but hurt either of them and he will come after you with his pockets full of explosive chemicals, his home-made tazer, and, if all else fails, his frenzied but anatomically-precise application of teeth, nails, and knees.
Robert Crais's Elvis Cole. Kidnap the son of his girlfriend? Elvis and his Psycho Sidekick Joe Pike will hunt you down to the ends of the earth and back again.
Damadora and Rana Sanga actually start a civil war because the Malwa empire was a threat to their families.
Nastily subverted in Rick Hautala's The Mountain King. The protagonist sees his daughter torn apart and eaten by monsters, but is too terrified to leave his hiding place.
In Death: Detective Sergeant Frank Wojinsky from Ceremony In Death. When his granddaughter Alice Lingstrom told him that she had been drugged and sexually exploited by an entire coven of Satanists and she had witnessed the leaders murder a young boy, he went Papa Wolf to try to take down the coven. Unfortunately, it made him sloppy and the leaders used the drugs Digitalis and Zeus on him, resulting in him dying of cardiac arrest.
Marcus, of Time Scout, will go through hell for his little girls. So will Armstrong.
As soon as he finds out Margo's his granddaughter, Kit becomes very protective of her. Skeeter, having tried to scam Margo before anyone knew, walks very, very carefully around both ever after.
The short story Monsters Tearing Off My Face has a particularly gruesome one. At the climax of the story, the little girl who drew the true picture of blue monsters tearing off her face turns out to really be a blue monster in a human disguise...when her mother tears it off of her, while her father tears the flesh from the bones of the foster parents who were about to rape her.
Buster Beasely in 1635: The Dreeson Incident. "I'm coming, Princess Baby!" To the rescue, that is. And does he ever, on a Harley and with a .45 and a knife.
Shellheart of Warrior Cats: Crookedstar's Promise is a Papa Cat, defending Crookedkit from his own mate. When she coldly tells him she blames her son for what happened to him, Shellheart is quick to defend him and breaks up with her. And when Rainflower tells Oakheart that Crookedstar would never be as good as him, Shellheart defends him with this:
Shellheart: Can't you keep your thoughts to yourself, just once?
Graystripe himself shows this in The Darkest Hour, helping his kits flee from Nazi-like TigerClan and attacking any enemy warrior that tries to hurt them.
In Felix Salten's Bambi's Children (yes, it's that Bambi), he sees a poacher taking aim at his son, and attacks.
In Tim Dorsey's novel Electric Barracuda Serge Storms is told that he's a father. Hint to the child molester on the playground: you really don't want to try to entice the child of a serial killer.
Charles Leeds, the husband and father of the second family of victims in Red Dragon, had his throat slashed in his sleep by Francis Dolarhyde. As he and his wife lay bleeding to death, Dolarhyde went down the hall to kill the children. With his throat cut open, artery spraying his lifeblood on the wall with every step he took, Leeds ran down the hallway after the killer and fought with him to protect his children.
Aral Vorkosigan does this rather cleverly for Miles in Vorkosigan Saga. He convinces the council of counts to charge Miles with treason rather then raising a private army in The Warriors Apprentice, knowing that the penalty for both is death but actual treason was in fact impossible to prove(he was guilty of raising a private army; that is he got out of a tight situation by manipulating his enemies into defecting to him).
Aral does this less subtly in Barrayar by ordering his private Sociopathic Hero, Bothari to protect Miles against Aral's own father. This caused an estrangement between them that lasted several years.
That same book also features one of the incredibly rare examples of Aral using his authority as Imperial Regent for personal purposes when he orders the Imperial Hospital to revoke his father's security clearances and lock him out, after the aforementioned father tried to kill Miles (who was at the time stuck in the hospital while the medics tried to minimize the damage from a poison he'd been exposed to earlier).
Though a husband rather then a father Captain Vorpatril has this toward Tej. It's a Barrayaran thing.
Lieutenant Panga in Someone Else's War will do anything, absolutely anything, to keep the children around him safe.
God in The Bible is this to his followers. A huge portion of the Bible is an endless loop of the Israelites being a Face Heel Revolving Door, being God-fearing one minute and worshiping idols the next. Yet every single time they cry out to God for help, he answers them.
Jesus inverts this in the New Testament. The one and only time he truly gets angry is when he goes to his Father's temple and finds it desecrated. He sits down, braids a whip, then (metaphorically) unleashes hell.
There's also her father Desmond who flings a mugger through a shop window for attacking his wife and infant daughter.
Although his relationship with Rue is never defined, Thresh is one towards her in The Hunger Games. When he overhears Clove taunting Katniss about Rue's death, his Berserk Button is pressed, actually breaks his calm demeanor and shouts furiously and it didn't go well for Clove.
Haymitch displays these traits from time to time regarding Peeta and Katniss.
Averted by Peeta's father. He seems like a nice man but he doesn't intervene when his wife hits his children. The books imply that she even whipped them at times.
In the Dale Brown novel A Time for Patriots, when the FBI agents hurt and threaten Brad, Pat pays them right back, forcing them to bug out.
Henry Grimm, in The Council of Mirrors by Michael Buckley, attacks Grendel (Yes, that Grendel) unarmed, and wins. He also beats up his much-loved brother in both cases to protect his daughters.
In The Dog Stars, the main character meets an old man living with his daughter on a farm After the End. It turns out that the guy is a former Navy SEAL and is more than capable of protecting her. The main character refers to him only as "Pops."