Yes - He features in a lot of different popular media and was first portrayed in H.P.Lovecraft's The Call of Cthulhu.

The mythology of Great Old Ones etc. is usually referred to as the Cthulhu Mythos, though Cthulhu is definitely not the most powerful being. (That honour would probably go to Azathoth - a blind, mad sleeping god who happened to create our universe as part of his dreams - don't wake him up!)

Im def a fan after South Park XD