Papa Wolf/Web Comics

Thespiphobia's Rich Gurney will MAUL YOU if you mess with his techies. Any other time, he's the sweetest, most harmless guy on the planet].
In Wigu, Quincy Tinkle may be a happy, somewhat dumb guy, but if Wigu or Paisley are harmed he will go to great lengths to get revenge. To date, Quincy has annihilated an alien insect that bit Wigu, fought off a group of Plesiosaurs with nothing but a knife when they attacked the Tinkle family van, and almost murdered Hamburglar after the latter hospitalized Wigu.
In Order of the Stick, Vaarsuvius' mate and children are threatened by the mother of a young black dragon the Order had slain earlier. Vaarsuvius makes a deal with fiends to gain enough power to not only kill the dragon but use an epic spell to slay every single relative that black dragon had. His/her mate was suitably horrified.
- Note that this example crosses over with Mama Bear.
- Also in Order of the Stick, Belkar Bitterleaf (v2.0) can turn into a Papa Wolf if you threaten his adopted cat Scruffy (see here). Don't push his Berserk Button. (Not that he has any other buttons.)
Ed in Digger appears, for a Hyena, harmless and non-violent, to the point he doesn't try to defend himself from or leave his abusive wife (hyenas are matriarchal, as is a major theme in Digger). That is, until his violent, mentally ill spouse started beating their daughter. This did not end well.
In The Inexplicable Adventures of Bob, Mook the Bigfoot Sasquatch and Yeti is this to his son Rocko, almost starting a war by way of overreaction when Rocko gets stood up for a date.
- Bob rarely loses his composure much beyond his stock look of Dull Surprise. We've seen him scared or frantic upon occasion, but the only times we've seen him furious are the times Jerry has threatened Molly with a gun. When Bob believed she'd actually been hit, he launched himself at Jerry (who was armed) and tackled him without hesitation.
The Shintulla Chieftain from Dominic Deegan gets royally pissed when Jacob apparently kills his son. Jacob's expression makes it perfectly clear that he knows he's screwed.
El Goonish Shive gives us Mr. Verres. Sure, he's a Reasonable Authority Figure, sure he's an endless barrel of exposition, and sure he's a little eccentric. But mess with his son, his niece, or any of their friends, he WILL blast you without warning or mercy.
Goblin Hollow: When gargoyles come after his goblins: Ben in action
Daisy Owl: Mr. Owl is a Papa Wolf, despite being an owl. He's willing to go up against NASA armed only with a bear if it means saving his kids.
Zombie of Hanna Is Not a Boys Name is usually a pretty mellow guy, but don't touch his friends. Ever.
- And you don't mess with him, either, or you'll have Hanna to deal with.
In Megatokyo, Ed learned the hard way that just because Ibara may be a jerkass that leeches money off his daughter Junko doesn't mean he takes kindly to having a shotgun pointed in her general direction.
In The Fancy Adventures of Jack Cannon we have that rare example of both parents being Badass and protective of their son. Not that he can't stand for his own.
In Exterminatus Now, Lothar Hex's adoptive mercenary father is fiercely protective of Lothar and his other foster son Kyle. He even threatened to cut out the hearts of the other main characters if anything happened to Lothar or Kyle because of their Inquisition work. Lothar is equally protective of his crazy mercenary family -- he and Rogue nearly killed each other when Rogue refused to believe Kyle selling weapons to cultists was just a stupid mistake and threatened to kill him and Lothar's dad.
Goblins has Pan, a blind ogre, fulfilling this role for Yala, a mute, disabled kobold who acts as his 'pilot'. Threatening Yala while Pan is nearby is a good way to get yourself brutalised, as the dwarf in this strip finds out to his cost.