Jerry Garcia appeared in the episode "Do the Handicapped Go to Hell?", as a resident of Hell.
He was also name-checked in "Ike's Wee Wee" by Mr. Mackey. When Jimbo tells him to go see a Grateful Dead concert, Mackey regrets that he can't because Garcia is dead.
Appearance
Like many celebrities in early seasons of the show, he appears with a photo cutout as a head.