The Adversary is an ancient mystical entity, possibly demonic in nature, who seeks to destroy the present universe and to create a new one in its stead. The Cheyenne Indians also refer to the Adversary as the 'Great Trickster', for the Adversary uses deception and trickery in attempting to achieve his goals. His native dimension is one of chaos, which the Adversary loves and seeks to spread to Earth's dimension, overturning order for the mere sake of doing so. The Adversary regards himself as a gamester, toying with the fate of the cosmos for sheer enjoyment. In his true form, the Adversary is not composed of physical matter; hence he can be fought successfully through magic but not through most forms of physical force. The Adversary is, however, known to be vulnerable to harm by cold iron, and hence to both steel and Adamantium.
The Cheyenne Indians have long known of the existence of the Adversary, and their shaman, the mutant technosmith Forge, was trained from birth to combat him. Forge's teacher was the older Cheyenne shaman Naze, who himself once clashed with the Adversary. However, Forge rejected the life of a shaman and instead enlisted in the United States armed forces. Years later, Naze was killed by a member of the alien Dire Wraiths, who duplicated his form. That Wraith, in turn, fell under the mystical possession of the Adversary. The false Naze convinced the then-powerless X-Man Storm that Forge had fallen under the influence of the Adversary and was attempting to destroy the Earth. The false Naze accompanied Storm to the mountain in the Western United States that was the "heart of his magic". The false Naze had Storm go up the mountain to stop Forge, claiming that he could not go himself since Forge had set mystical alarms and defenses against him. Storm fought off the demons that attacked her and then stabbed Forge, only to learn that he was actually attempting to close the dimensional gateway through which the demons were coming. Forge and Storm both fell through the gateway and were transported to the Earth of a parallel dimension on which apparently no other human beings existed. Thus the Adversary had rid himself of the two people he regarded as the only real threat to his plans to destroy and remake the universe. He offered them the chance to become the "world spirits" of the new Earth he planned to create, and to be the parents of its new human race.
The Adversary had, by now, captured Roma, the goddess who acts as the guardian and caretaker of the known dimensions and held her prisoner within her own Starlight Citadel. Forge restored Storm's ability to use her superhuman powers and they escaped the world to which they had both been exiles, only to be captured by the Adversary. On Forge's native Earth, the Adversary had jumbled elements of many different time periods at Forge's Eagle Plaza headquarters. The X-Men fought against the resulting chaos while their actions were televised across the world by reporter Neal Conan. The X-Men, their ally Madelyne Pryor, and Conan were all transported to the Starlight Citadel where they distracted the Adversary, who had abandoned Naze's form and revealed his true appearance, whilst Forge and Storm regained their freedom. The X-Men and Pryor willingly agreed to sacrifice their lives so that Forge could cast the spell needed to defeat the Adversary. In casting the spell, Forge transformed the X-Men and Pryor into beings of pure energy which he then gathered together and hurled at the Adversary, forcing him through a mystical portal known as the Great Gate which closed on him. According to Forge, the deaths of the X-Men and Pryor had assured that the Adversary would be sealed away for all time. However, Roma then used her great powers to return the X-Men and Pryor to life. Roma explained that the Adversary must not be thus confined forever, since through the chaos he brings can come positive change and growth.
The Adversary returned once more thanks to the seer named Haven, who was pregnant with a sentient mutant foetus. The Adversary used the foetus as a vessel with which to rematerialize in the mortal realm, killing Haven in the process. The Adversary was defeated by Forge once more after the mutant reclaimed his mystic heritage and combined it with his technological prowess.