Jordan Boone was once a scientist for the powerful company named Alchemax and was a respected member of the corporation. However, he sought to gain powers and sneaked into the company's Aesir program; an attempt to create new versions of the old Norse gods. The subjects of the program were granted powers, but at the cost of losing their identity due to a computer chip placed in their brains which made them believe that they were the true Norse pantheon. Boone however was able to avoid getting the chip, and he was transformed into the shapeshifting god of trickery, Loki. Then he moved to the floating city called 'Valhalla', which was seemingly shoddily built and thus endangering any innocents in the city below.
The X-Men became involved because Meanstreak was friends with Boone at the time and had become concerned over his disappearance. Meanstreak brought several of his teammates with him to New York. They broke into Boone's apartment in order to look for clues. The break-in was accomplished because Boone and Meanstreak had designed their own security systems in order to avoid the ever watchful eye of Alchemax. Meanstreak discovered Boone's personal journal under his award his Richards Foundation award for theoretical physics. Boone was investigating Paul Phillip Ravage, who would later become the 2099 hero simply known as Ravage.
The X-Men appeared on the scene along with Doctor Doom, Punisher and Spider-Man of that time period. Boone helped them to take down the program and then escaped.
When he was seen next, Boone was taken into custody by Desdemona and Lytton Synge, the owners of the Synge Casino, because they thought he was a member of a gang conspiring to cheat. They attempted to torture the names of Boone's accomplices out of him, only to cause his ability to go haywire, revealing that he was in fact the entire "gang". Boone escaped and transformed from the Loki persona, which he now saw as useless, into the devilish Halloween Jack and went about creating a plan to get back at the Synge siblings and take over Las Vegas in the meantime. In order to accomplish this, he enlisted the help of Meanstreak.
Meanstreak agreed and followed Jack to Las Vegas where they encountered their old rivals--the owners of the Synge Casino. First, Jack, with the technological help of Henri, transferred most of their fortune into his own bank account and then ousted the siblings in order to gain control of the casino. In the weeks to follow, Jack unveiled his plans to unleash a Virtual Unreality Projector upon the city, warping it with energies from another dimension. Meanstreak helped him construct this machine and they actually started it, but President Doom arrived and shut it down because of its instability. Jack had meant to allow the device to warp the whole planet into a state of chaos, but President Doom surrounded the city with EMP devices which quarantined the city.
Halloween Jack supposedly died, but made an unexpected appearance on Earth-616. He was somehow pulled from the timestream before his death and redeposited in the present, where he pestered Domino.