Superfunk's best friend since kindergarten. In some ways Jack serves as Superfunk's conscience, such as when Superfunk had an irrational mistrust of the Cook-O-Matic 3000. Jack is the voice of reason in the group, but not in an annoying, told-you-so sort of way. Usually, he lets the others learn their lessons themselves.

Jack was adopted by Grace and Morty Guynan. He remembers nothing of his Korean background, but his parents go to great pains to celebrate the official Korean holidays, with the appropriate costumes and proper Korean pronunciation. Jack thinks they're more into it than he is. But he considers himself a citizen of the world, including having an on-line German "girlfriend" named Helga. His friends are dubious about her existence, but Jack swears it's true.