References.
For the person who was the original Jack O’Lantern, see Hobgoblin. For the second Mysterio, who also used the Jack O’Lantern identity and was the first to use the name Mad Jack, see Mysterio (Berkhart). For later Jack O’Lanterns see Jack O’Lantern (Levins) and the current Jack O’Lantern.
Continuity Note
The “Mad Jack” Identity was created by J.M. DeMatteis without any idea of who he would end up being, and this was not resolved before DeMatteis left Spectacular Spider-Man. Tom DeFalco would later pick up the dropped plot line for his mini-series Spider-Man and Mysterio. In that mini-series, Mad Jack variously claimed to be the deceased Quentin Beck, and the second Mysterio Daniel Berkhart. At the conclusion of the story, Mad Jack was revealed to be Maguire Beck, cousin of Quentin. However, the story also ended with the reveal that Berkhart was indeed involved, (The Handbook of the Marvel Universe would later confirm that he had indeed had been the first Mad Jack as described by Maguire) and that the appearances of Mad Jack and Mysterio in the story were some combination of Berkhart, Maguire Beck, and robot duplicates in various costumes, aided by illusory effects. Therefore then the appearances of Mad Jack in Spectacular Spider-Man, which all occurred before Quentin’s death, should be attributed to Berkhart, with Maguire taking the Mad Jack role and Berkhart taking the Mysterio role subsequent to Quentin’s death.
It should be noted that, even after Maguire began to act directly as Mad Jack, the nature of the illusions involved and her collaboration with Berkhart make it difficult to attribute specific actions to her or Berkhart.
History
Maguire “Terry” Beck is the cousin of the Spider-Man enemy Mysterio. Growing up, she idolized her cousin, following his career first in film, and then in crime. She followed in his footsteps, leaning the trade of special effects, though her specialty was in digital effects rather than Quentin’s practical effects. Quentin also taught her the trade secrets that he used as Mysterio, and Maguire hoped that he would ask her to be his partner in crime. In the meanwhile, she worked as the partner of Daniel Berkhart, another of Quentin’s students who had taken up the identity of Jack O’Lantern/”Mad Jack.” Magurie provided him with tech support and recon through a robotic cat that Berkhart jokingly called “Maguire“
After Quentin’s suicide, Maguire devoted her life to eliminating anything that in some way “wronged” her cousin. She and Daniel Berkhart hatched a scheme to attack Spider-Man, Daredevil, and J. Jonah Jameson Maguire took up Berkhart’s former “Mad Jack” persona, while he once again assumed the role of Mysterio. At first posing as Quentin returned from the dead, she and Berkhart used the Mad Jack and Mysterio personas to attack their enemies. She trapped Spider-Man, Daredevil, and Joe Smith in “joy juice” while tormenting Jameson and Smith’s girlfriend Betsy, who had been marketing Mysterio’s image after his death. Daredevil and Spider-Man escaped, fought against her illusionary avatar, and found her hidden behind a computer terminal, apprehending her and turning her over to the authorities, although Berkhart was not discovered or apprehended.
A later Jack O’Lantern later claimed to have killed off all the other villains who had used the name, though as Maguire had only used the Mad Jack variant of the persona, and was presumably still in prison, it is unknown is this includes her.