BIOGRAPHY
Gregory Terraerton grew up in Melbourne, Australia with a comfortable home and a loving and wealthy family. He was also a grinning sadist who loved murder and went off to become a mercenary. Nicknamed Slayback, he was one of several test subjects for Canada’s Department K when they revisited the Weapon X Program to create a Canadian super-soldier. This version of Weapon X ran several parallel experiments. They had access to genetic material from the original Weapon X, Logan, and found ways to reverse engineer his healing factor. However, Department K also worked with cybernetics, providing replacement body parts to those who needed them. Terraerton was a rare attempt at combining both programs, infusing his body with a healing factor while also reconstructing most of his head, arms and other mass with mechanical prosthesis.
The Weapon X Program’s mercenaries operated together briefly as a squad once their upgrades were considered effective. Slayback worked with Garrison Kane (a young merc turned into a cyborg after losing his limbs in an explosion), Wade Wilson (who accepted the healing factor as an opportunity to beat terminal cancer) and the burly Bernard “Sluggo” Hoyster. Wilson and Terraerton were comrades and perhaps technically friends, but there was a current of animosity beneath the surface. Wilson was a soldier, able to turn off his humanity and kill at will when the job called for it, but he recognized Terraerton was a psychopath who enjoyed killing. He was also good at it, making Wade afraid to find out what would happen if they ever had to fight each other.
Somehow, they had a falling out on a mission. The details are scarce, but Wilson apparently set off an explosion which tore Terraerton apart. Wade saw the body himself and there was no way anything human could recover from being scattered and opened up like that. It took ten long years for Slayback’s body to pull itself back together. His body was still a deadly weapon, but nowhere 
near his peak. His skin was yellowed and decayed while his cybernetics sparked with corroded metal and glitches. Terraerton was fixated on Wilson and taking his revenge over leaving him for dead. Slayback infiltrated the records for Department K in order to get updated information on his targets. In his search for Deadpool, Slayback shook down Kane, the program’s graduate who had officially become the new and sanctioned Weapon X in his absence.
Slayback returned during the quest for Deadpool’s late employer Tolliver’s final legacy. He got 
ahead of Deadpool’s investigation to the Palace of Tomorrow Hope in Nepal. The first to arrive, Terraerton found and grabbed Wade’s ex-girlfriend Copycat, also on the hunt. Slayback was gleefully reunited with his prey, dishing out ten years’ worth of hatred on Deadpool. Wade actually panicked when he saw Terraerton, something Slayback found delicious. He started tearing into Deadpool and only paused for a moment when Copycat threw herself onto Slayback’s incoming spike to save Wade. Terraerton couldn’t even process the idea that someone would sacrifice themselves over a failed love like Wade and Vanessa’s.
Their conflict ended when Deadpool’s sidekick Weasel activated the true prize from Tolliver’s will, an ADAM Unit from almost 2,000 years in the future. ADAM Unit Zero was programmed as a peacekeeping mechanism, the ultimate weapon being one able to disable all other kinds of weapons. Once activated, Zero’s biosanctuary parameters authorized and empowered him to neutralize all weapons of war in his area. Slayback was scanned as a biological, technological and psychological weapon of war, a clear judgment for nullification by Zero. The android merely waved his hand and Terraerton’s augmentations ceased to function before he was apparently disintegrated on the spot, his vendetta aborted and irrelevant to the peacekeeper. [Deadpool: The Circle Chase #1-4]
Despite this, Terraerton pulled himself back together much faster than last time. Slayback got back to work as a mercenary, though his obsession with Deadpool remained. He was employed by a genetics initiative interested in discovering a cure for the Legacy virus so they could market it for rich buyers. They targeted Deadpool for abduction in order to study his healing factor as a possible avenue for research and Slayback eagerly took the mission to capture his old rival. Once Wilson was secured, Slayback was deployed to capture Maverick, a mutant already infected with the Legacy virus and imprinted with an artificial version of Wolverine’s healing factor, making him an ideal test subject. Unfortunately, the old soldier fared better than Deadpool and escaped after catching Slayback’s telescoping arm in an elevator door. Gruesomely, the arm continued grasping for Maverick, even as he made his escape.
Back at the Niagara Falls research facility, Slayback amused himself by playing Tic-Tac-Toe on 
Wilson’s regenerating flesh while waiting for his next assignment. Meanwhile, Maverick gathered intel on the situation and recruited Wolverine to rescue Deadpool and shut down the researchers before they came after them. Once North and Logan got inside the facility, Doctor Westergaard abandoned Slayback and set the self-destruct sequence. The trio from Weapon X leapt to freedom just as the laboratory exploded, leaving Slayback behind in the blast to die. Surely. I mean, surely. [Wolverine Annual ‘95]
Many people hated Deadpool, and Slayback eventually picked up a contract from disgraced former FBI agent Allison Kemp. Agent Kemp hated Deadpool ever since he blew up an arms deal while she was undercover, leaving her in a wheelchair for life. Over the course of years, she siphoned billions of dollars from the federal government before her retirement. She used the money to fund a makeshift helicarrier and hire Slayback and T-Ray as muscle to help her finally kill Deadpool. Kemp spent years studying Deadpool’s tactics and psychosis, but Wilson lost his 
healing factor shortly before her scheme began, leading him to change his M.O. now that he was effectively mortal. Slayback and T-Ray spent days training in Kemp’s interactive holo-programs until they learned Deadpool had infiltrated their mobile sky-base. When the engines shut down, Slayback tried to save himself by parachuting to safety, only to learn that Deadpool rigged the parachutes to explode. Terraerton completely missed out on the final confrontation with T-Ray and Kemp, on account of being dead. Again. [Deadpool (3rd series) #61-63]
Slayback recovered slowly and got back into the field, overseeing mercenary ops for the Arcadia 
Corporation, their scientist Abraham Cornelius and his Paradise research facility. Slayback’s mercs attempted to secure the site after Wolverine killed Cornelius and then died himself while freeing some of the test subjects. Instead, Major Sharp and several of the experimental mutates gathered to make their escape in Slayback’s own helicopter. Sharp demonstrated his enhanced tactical awareness by overcoming Terraerton and his distending limbs, stabbing the more powerful Weapon X graduate in the heart. [Death of Wolverine: The Weapon X Program #1]
Slayback died, again, and even appeared in the Realm of the Dead when it was thrown into chaos after the abduction of Mistress Death. Deadpool and Thanos were unlikely allies trying to restore the natural order, but their presence in the afterlife was like catnip to their victims. Deadpool was thrilled for the opportunity to kill Slayback all over again. [Deadpool vs. Thanos #3] True to form, death could not hold Terraerton and he eventually crawled his way back to the realm of the living. 
Slayback was one of numerous mercenaries who attacked Deadpool and his Mercs for Money when they took possession of a Rigellian Recorder infused with knowledge of the future. By this point, Deadpool was hardly afraid of his old nemesis, having become quite confident that he could beat Slayback, even if he had to kill him over, and over, and over… [Deadpool and the Mercs for Money (1st series) #4]