Hemingway is a fictional villain created by Marvel Comics for their team called Gene Nation. His first appearance was in Generation X #5. He is one of the few members to remain in all three incarnations of the team.
On the anniversary of the Mutant Massacre, a horrific event in which Mr. Sinister's henchmen the Marauders killed many Morlocks, the members of Gene Nation reappeared in the main universe (Earth-616). Their mission was to destroy one hundred humans for every Morlock life that was lost, and also, in a side mission performed by Hemingway and Marrow, to kill some of the original Morlocks. In Marrow's eyes, Leech, one of the few to survive the massacre, was weak and instead of defending his people he hid like a coward. Fortunately, the White Queen, who was trying to recruit Leech to her teenage mutant team Generation X, was able to thwart their efforts. However, with the intervention of the Dark Beast Marrow and Hemingway escaped.
Afterwards, a team of X-Men and the Morlock Callisto confronted an attack group from Gene Nation, which included Vessel, that was threatening the lives of several civilians by attaching incendiary devices to them that were regulated by Marrow's heartbeat. Seeing it as the only way of stopping the terrorist, Storm ripped out Marrow's heart. Defeated, Callisto took Vessel, along with the remaining members of Gene Nation, back to The Hill.
A few months later, Storm was kidnapped by Mikhail and taken to The Hill. Once there, she had to fight her way to the top of the hill where Mikhail lived, where she successfully overpowered him. Hemingway was one of the team that had successfully reached the top, yet he had decided to take on the moniker of "Pain". Having won the victory, Storm forced Mikhail to take all of the people living on The Hill back to the real world. In an effort to give the mutants a new start, she settled them in a village outside of her home town in Africa.
However, they wouldn't get much of a chance to start over because shortly after they were placed in Africa the Dark Beast gathered some of the original members of Gene Nation, along with some new recruits, to form a new team. The express purpose of this team was to capture test subjects for the evil genius, namely the students of Generation X. Now returning to his former name, Hemingway, along with Vessel, were the only members of Gene Nation to be unsuccessful in their quarry, the newcomer Gaia. Along with the White Queen and Nate Grey, also known as X-Man, the three defeated the team.
Hemingway's final appearance was in the pages of Weapon X where he joined his old teammate Marrow, who was now leading Gene Nation, as her personal bodyguard. After manipulating the perfect killing machine Agent Zero into unintentionally killing his former sidekick, the assassin hunted down and killed every single member of Gene Nation in an act of vengeance, Hemingway being among the last. However, he spares the life of Marrow because he does not want others to see her as a martyr.