Not to be confused with Grandpa, Greg's living paternal grandfather.
Grampa is or was the father of Susan and the husband of Gramma, whom most likely divorced Gramma or died. He was shown in the extended Do-It-Yourself Book, in Greg's family tree.
In Greg's family tree, Grampa is half-bald with a few strands of hair on his head. He wears glasses and is shown wearing a suit and tie.