Some random gag character in the Marvel Universe that is somehow pretty popular and incredibly powerful.
The fact that Marvel even made a character like Squirrel Girl shows how they either aren't aware that Rule 34 exists or don't care enough to think twice.
After discovering dat "Phat Gus" was "not a dude" (said gray chatterer was so roly-poly --- and had such a prodigious appetite --- due to being FULL OF BABIES, not from overeating), Mark Rober renamed his small furry "girl-squirrel" friend "Phantastic Gus".