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.
In Wyrd Sisters 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.
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. 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.
Nimitz 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.)
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. 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 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.
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.
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.
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.
Dallas's reaction to Finding out Johnny was dying from his burns. 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 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.
Howl is this after his son Morgan was threatened. He punched the guy twice. 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.
Caine. Even if you're a god, fucking with Faith will get your ass beat.
Harry Potter: James Potter. It may not have worked, but he was willing to risk certain death against Voldemort if it gave Lily and Harry time to run.
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.
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 a 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?
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.
Lieutenant Panga in Someone Else's War will do anything, absolutely anything, to keep the children around him safe.
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.
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.