For the person who was the original Jack o'Lantern, see Hobgoblin. For the second and also current Jack o'Lantern see Jack o'Lantern.
Macguire "Terry" Beck is the cousin of the Spider-Man enemy Mysterio. After his suicide, Terry devoted her life to eliminating anything that in some way "wronged" her brother. Originally as the Jack o'Lantern, she took the identity and re-established herself as Mad Jack.