Be they living or dead. Given that the Simpsons holds the world record for the highest number of guest stars, probably half of Hollywood has been on the show at one time or another. Still, there’s folks who can’t appear (because they’re dead) or haven’t been asked/refused to be on. So who would you like to see who hasn’t been a guest as of yet and what part would they play?
I personally, think that Orson Welles would have made a great father for the Comic Book Guy. Anton La Vey would have been hysterical as Bart’s spiritual advisor, and William S. Burroughs would have been absolutely priceless as a teacher or camp counsilor or teacher.