See Earl for other uses of the name
Cousin Earl is a syphilitic, one-eared member of an upper-crust British family in which Stewie finds himself born into when he stops his own conception in "Chap Stewie".
During a family night in the uncensored version of "Chap Stewie", Stewie is put in the spotlight to perform a song. Without having time to prepare something appropriate, he chooses to perform the theme to Wayne's World. His performance so appalls the family that his is banished to the attic with syphilitic Cousin Earl.
Cousin Earl is voiced by Seth MacFarlane.