Hemingway was initially introduced as a member of the sub-terranean dwelling Morlocks. He was believed to have been killed when Colossus' & Magik's insane brother, Mikhail Rasputin , flooded the subway tunnels that the Morlocks inhabited. Although, as is well-known, the eldest Rasputin narrowly rescued most of his would-be victims from drowning by opening a transdimensional portal that led to The Hill. The Hill is a unique dimension where time moves several times faster than in the mainstream Marvel universe (Earth-616).
Mayor Story Arcs
While they lived here, 10-20 years had passed, while mere months had passed in this reality. During this time, Mikhail trained these mutants into killing machines, and formed a team called Gene Nation. This team resurfaced in the mainstream reality on the anniversary of the Mutant Massacre. They were charged with the duty of brutally slaying one-hundred humans in retribution for each Morlock life lost. Hemingway and Marrow were teamed-up together to fulfill a different task. The duo was given the responsibility to kill some of the remaining Morlocks for abandoning the deceased. Marrow was of the opinion that Leech should be the first to die, as (in her eyes) he could have saved many due to his ability to disrupt the mutant X-factor, but instead he fled for his life. Fortunately for Leech, Emma Frost had decided to recruit him for the ranks of Generation X. Due to this fact, she was present when Leech was initially confronted, and defeated both attackers easily. As she was finishing them off, Dark Beast intervened allowing for their escape.
Shortly after, a small group of X-Men, accompanied by Callisto (former leader of the Morlocks), led an attack against Gene Nation to stop them from killing more civilians. As they fought, Storm ripped out Marrow's heart. Callisto, having certain maternal instincts toward Marrow, switched sides at the last moment and fled back to The Hill, with the surviving Gene Nation members.
Another short time later, Mikhail returned to capture Storm and forced her to answer for her crime. She did so by fighting each Gene Nation member individually from the bottom of The Hill, working her way upwards with each defeat. One of the mutants she faced was Hemingway, under the moniker of "Pain." Storm won her way toward the summit and eventually defeated Mikhail, forcing him to transport all of the remaining Gene Nation members (and herself) back to Earth-616. Her intention was to afford the brainwashed mutants a new start and settled them in a small encampment near her African home. This arrangement would be short-lived, however (for thanks again to the intervention of Dark Beast) many of them were captured along with new recruits in order for Dark Beast to create a new team. He would use this team to capture members of Generation X to be lab rats. Hemingway (for he had reverted to his former code name) and Vessel were the only members unable to successfully capture their target, Gaia. Since she was a fairly new member, they were unprepared for the extent of her vast powers, and were defeated with the help of Emma and X-Man.
Weapon X and Death
Later, Marrow (whom was able to generate a new heart thanks to her abilities) was found to be the new leader of Gene Nation. She hired Hemingway as her personal body guard. The newly reorganized team immediately resumed their dastardly ways by tricking Maverick into killing his former engenue, Bolt. In an act of extreme vengeance, Maverick tracked down and slew each and every surviving member of Gene Nation, save Marrow. Hemingway died in the line of duty, defending Marrow to his death.
Hemingway was among the many mutants resurrected by Selene & Eli Bard via the Transmode Virus during Necrosha. His current whereabouts are unknown, but most likely he returned to his dead state after Selece was defeated. Since he had his powers after he was resurrected, he was among the 2% of mutants to retain their powers post-Decimation.