BIOGRAPHY - page 3
When the Scarlet Witch altered history and created the House of M reality, she inadvertently released Mutant X on the world again. Just as before, Moira MacTaggert discovered her son Kevin possessed vast mutant powers that were eating away at his body, and tried to cure him of this affliction. In the House of M, however, any attempt to "cure" mutation was a capitol offense, and Magneto's Sentinels destroyed Moira's lab on Muir Island, making her a wanted fugitive and setting Kevin loose to kill as he pleased. Mutant X soon became an infamous Scottish serial killer known for the desiccated corpses he left in his wake.
Kevin made his way to Manhattan, killing at his leisure while looking for a body strong enough to sustain him for an extended period of time. He used the body of club bouncer Blunderbuss to get access to the model Angel Salvatore. Doing so caused him to cross paths with the Exiles, who he immediately sensed were "different" from others. The Exiles had been dimension-hopping with Beak, a native of Earth-616, who returned during House of M to find his reality altered and his children with Angel no longer existed. Mutant X kidnapped Beak to find out more about the Exiles, and they in turn were approached by Moira who informed them about Kevin's murderous history, powers and weaknesses.
As Proteus, Kevin confronted the Exiles in Angel's body and scanned their minds to learn where they had come from. Once he recognized the purpose of the Tallus on Sabretooth's wrist, he interfaced with the device and somehow managed to access the Crystal Palace's dimensional records, "downloading" an enormous amount of knowledge about parallel dimensions and how he could access them with his powers. Moira shot "Angel" with her pistol but, as the metal forcibly drove Kevin from Angel's body early, he advanced on his mother as his next host. Moira chose to shoot herself in the head rather than become her son's next victim. The Exile named Mimic seemed like an ideal candidate for stopping Proteus (since he had copied the organic metal of Colossus), but had recently sworn an oath never to kill again. He charged Proteus in his vulnerable energy form and prepared to deliver the killing blow, but Proteus psyched him into hesitating just long enough. Proteus unraveled Mimic's metal and leapt into his body, taking Cal as his latest host. With that, Proteus abandoned the House of M, leaving the horrified Exiles to give chase in hopes of saving their friend. [Exiles (1st series) #69-71]
Thanks to the information from the Crystal Palace, Proteus found his way to a version of the New Universe shortly after the "White Event." He intended to locate Ken Connell and use his Starbrand enhanced physiology as an unstoppable host body. The Exiles anticipated Proteus' target and redirected Connell before he went home, but another paranormal found Proteus instead: John Tensen, the so-called Justice Warrior. Although Justice wasn't his intended target, Proteus was eager to move on from Mimic: Cal's body was sturdier than most thanks to his healing factors copied from Deadpool and Wolverine, but his mind was stronger than Proteus anticipated. Kevin was experiencing bleed-through from Calvin's love of Blink, as well as the suicidal urge to transform into Mimic's metal form. So, taking advantage of Justice's arrival, Proteus abandoned Mimic's husk and jumped into Tensen.
After learning of Mimic's demise, the Exiles regretfully refocused their mission from rescue to elimination. Researching the paranormals of that world, they came up with a plan. With the help of the sleep-inducing Lenore Fenzl, they rendered Proteus unconscious so that Keith Remsen, Nightmask, could use his dream-walking abilities to pacify Kevin. The plan ultimately proved ineffective, and Proteus was only stopped from killing them all by the Exiles' newest recruit, Longshot. Longshot's famous "luck" acted as a shield against both Proteus's reality-warping powers and his body-snatching, and his precision metal throwing knives made him an unexpected threat. Proteus fled the New Universe in Justice's body to avoid further conflict. [Exiles (1st series) #72-74]
In the future of 2099, Proteus emerged through the Virtual Unreality portal at Alchemax controlled by Jordan Boone. Seeking information about this world, Proteus pressured Boone into helping him find a perfect new host. 
Boone identified the Hulk of 2099, who was in town for a meeting with Stark-Fujikawa in his human identity as John Eisenhart. Proteus and Jordan crashed the meeting, and Kevin abandoned his Justice host in favor of the much stronger Hulk 2099. When the Exiles and Spider-Man 2099 arrived, Proteus forced all the heroes out of the building, except Blink. Even two hosts later, Proteus was still feeling Mimic's love for Clarice, and tried in vain to express his feelings for her. Although representatives from the Megacorps arrived and made several offers to help Proteus sustain his form indefinitely, Kevin relied on Spider-Man and Boone's assertions that the Megacorps were fundamentally untrustworthy and would use him as a lab rat. Proteus abandoned the 2099 timeline without taking any of the offers. [Exiles (1st series) #75-76]
Changing tactics, Proteus jumped to Earth-S where he set up a trap for the Exiles. By befriending the Squadron Supreme and aiding them in battle with the Blue Eagle corps, Proteus convinced the Squadron that he was being unjustly hounded by the Exiles and their desire to "meddle" with the natural course of events in different realities. A fight between the Squadron and Exiles broke out when the latter arrived, freeing Proteus to move on unmolested. [Exiles (1st series) #77]
In a world defined by a post-nuclear holocaust and ruled over by an amoral older Hulk called the Maestro, Proteus tried for his next body. Thinking a more powerful Hulk would be the perfect "trade up," Proteus intended to claim the Maestro as his next host. The Exiles managed to get ahead of Proteus this time, however, and warned Maestro of the body-thief. Unfortunately for the Exiles, their alliance with the Maestro didn't survive past the first poorly aimed throwing knife, and a three-way conflict broke out between the parties. On the plus side, even Proteus' Hulk body started to decay due to the continuous exertion. The Exiles had protected themselves along the way by having small metal strips surgically implanted in their heads to keep Proteus out. 
When Morph bulked up and battled the Proteus-Hulk 2099 hand-to-hand, however, Proteus struck him so hard that his spongy body ejected the metal strip, leaving him vulnerable to the killer. Proteus seized the opportunity and possessed Morph, finding the malleable shapeshifter a surprisingly perfect fit. Morph's body showed no signs of breaking down at all, meaning Proteus had found a permanent home for his energy form. [Exiles (1st series) #79-80]