Cthulhu? He's a powerful being from the works of H.P. Lovecraft. Capable of unimaginable destruction, worshiped as a god by a cult of mortals inhabiting the planet where he happens to spend his dormant time, etc.

Picked up by fans for lots of games, references, etc. Call of Cthulhu, for example. But he pops up in all sorts of random places. Web comics, etc. One of the celebrities of geekdom.

There is, of course, a decent-sized wiki article about him as well as a separate, equally long article listing his appearances in popular culture . Maybe skim over those, see if anything sparks a more specific memory?

When in doubt, think about penguins. It probably won't help, but at least it'll be fun.