Jack 'O Lantern used to be a rascal in a medieval village whose tricks and pranks ranged from harmless jokes to cruel acts. He is the main antagonist of Gumball's Jacked-Up Halloween. One day, the towns people couldn't take it anymore and devised a prank of their own and sent it to the queen (knowing that the queen had no sense of humor) and signed it from Jack. When the queen opened the gift from "Jack", she sent a knight out to kill him. The next day, the Grim Reaper went to reap his soul but Jack stole his scythe and would only give it back if Grim had granted him immortality. When the deal was done, as punishment, Grim decapitated him.
Later on, Jack got himself a pumpkin and wore it as his new head. He still lives in his old house untouched by time and every Halloween night, Jack emerges with a sack full of trick and plays terrible pranks on the people of Megaville.