The two having shared a cell in prison together, Berkhart was trained in arts of illusion by the original Mysterio himself. While Quentin Beck had faked his death, Berkhart was hired by J. Jonah Jameson to convince Spider-Man that Berkhart was the Ghost of Mysterio. With Maguire's assistance, took up the mantle of the Jack O'Lantern (preferring to call himself "Mad Jack" to differentiate himself from the others to have taken up that role). Several years later, Mysterio did die for real and Berkhart decided to take on the role of Mysterio on a full-time basis with Mysterio's cousin Maguire providing tech support and adopting the Mad Jack persona in his place. As Mysterio, Berkhart battled Spider-Man and Daredevil, and joined the Sandman' s Sinister Six.
Jack O'Lantern later claimed to Venom that he had killed the previous users of the Jack O'Lantern identity, including presumably Berkhart.
The character was created by Gerry Conway and Ross Andru and first appeared in The Amazing Spider-Man #141. The character was brought back over 20 years later when Mysterio died for real, although his return was mostly to fix continuity, giving an explanation to appearances of Mysterio after Beck's death and the unresolved "Mad Jack" storyline in Spectacular Spider-Man.
Major Story Arcs
Berkhart hired a certain villain by the name of Armada to steal a revelutionary new D.I.T (Digital Imagery Transmission) chip, which can emit thoughts as holographic images. He buys a TV station as Randolph Hines and turning it into an overnight sensation by hypnotizing his viewers into "MysteryVision" addicted zombies.
I Hate a Mystery (Civil War)
He was last seen teaming up with Spider-Man to battle Francis Klum who had also started calling himself Mysterio. This led to the confrontation between both men as well as the demonic spirit of the original Mysterio. Whereas Klum possibly died and the original Mysterio eventually returned, Berkhart hasn't been seen since.
- Mad Jack was featured in ToyBiz's Spider-Man Classics line.
Powers & Abilities
It is presumed Berkhart had the same abilities/skills as Mysterio. Mysterio had no actual superpowers, though he is a very accomplished illusionist, athlete, and hand-to-hand combatant. Their main threat came in the form of advanced technology mixed with great skill at illusion. Gadgets of his have included spring-heeled boots, hologram projectors, radar sensors, and various hallucinogenic gases (including a gas that could nullify Spider-Man's spider-sense), among other things.