Jack O'Lantern is one of the many guest characters from the show, The Grim Adventures of Billy and Mandy, on Cartoon Network. He appeared as the main villain from the Billy and Mandy special, Billy and Mandy's Jacked Up Halloween. Jack was once a normal human until he got a lot of heat in the town of Endsville for pulling off pranks. One day, Grim decided that he couldn't handle Jacks' pranks, so he chopped his head off with his scythe. Jacks' body somehow managed to gain consciousness, so he grabbed a pumpkin and he uses it as his new head. As a pumpkin headed freak, he still plays terrible pranks unknown.
In the special, he was voiced by Wayne Knight. In the game based on the show, he was voiced by Maurice LaMarche.