Katrina Luisa van Horn grew up to be a champion skier for an unnamed Eastern European country. When competing in the Winter Olympics for the first time, Van Horn overheard a male rival, Karl Lubbings, denigrate women athletes. Van Horn challenged Lubbings to a race that night, but in the course of the competition, Lubbings abruptly cut van Horn off as they skied down the mountain. In the resultant fall, Lubbings was killed and van Horn was crippled.
Van Horn was driven nearly insane by bitterness and anger, and her plight was soon discovered by agents of the subversive scientific organization called Advanced Idea Mechanics (A.I.M.). Operating covertly, A.I.M. financed a militant feminist group that recruited van Horn, and the organization also secretly funded her lengthy rehabilitation process. Moreover, van Horn, who adopted the code name "Man-Killer," was outfitted with a powerful exoskeleton that granted her superhuman strength. As Man-Killer, van Horn embarked on a campaign of terrorism that began with the assassination of a strongly anti-feminist Chicago mayoral candidate. In the course of this attack, van Horn encountered Greer Nelson in her original costumed identity as the Cat, but she swiftly subdued her and escaped. Journeying to New York City, Man-Killer carried out a plan to steal fissionable radioactive material from a Harlem power plant, only to be opposed by both Spider-Man and the Cat, who had followed her to New York. Man-Killer ultimately surrendered after the Cat confronted her with the fact that her A.I.M. benefactors had been men.
Man-Killer was soon freed under the auspices of a splinter group of the terrorist organization Hydra. This cell had come under the leadership of the Maggia crimelord Silvermane, who filled the section chief positions with costumed criminals. Van Horn was herself appointed the head of HYDRA's assassination division. However, Silvermane was ultimately out of his depth running HYDRA, and his organization's headquarters was soon invaded by Daredevil, the Black Widow, and agents of SHIELD. Man-Killer herself was captured after the Black Widow's ally Ivan Petrovich affixed a device to her exoskeleton that deactivated it.
Van Horn was freed from custody months later by Justin Hammer, who financed the reconstruction of Man-Killer's armor in exchange for a percentage of any profits she might make as well as her loyalty. Van Horn was part of a small army of supervillains in Hammer's employ who were pitted against Iron Man aboard Hammer's floating villa near Monaco. Like the other criminals present, Man-Killer was summarily defeated by Iron Man, though she managed to escape European authorities soon afterwards.
Van Horn recruited a new gang of militant feminists and sought to increase her group's credibility by freeing Hildy Dawes, a former underground terrorist leader who had surrendered to the authorities after years as a fugitive. Despite the opposition of Spider-Man and the She-Hulk, Man-Killer managed to escape with Dawes. However, Dawes had no desire to escape, and, hoping to atone for her own terrorist actions, used an exposed power cable to apparently electrocute both herself and Man-Killer.
Though believed dead for many months, Man-Killer was apparently alive and in hiding during this time. At some point, she was contacted by the Crimson Cowl and invited to join the sixth incarnation of the Masters of Evil. It is unclear whether or not the Cowl was responsible for Man-Killer's development of actual superhuman strength without apparent artificial aids. The Masters took in mercenary work to raise funds for the Cowl's worldwide blackmail scheme. Acting as security for the so-called Arms Merchant, the Masters battled the Thunderbolts, who were themselves members of the fourth Masters of Evil in heroic guises, and the Black Widow. Though they failed in their assignment, the Masters escaped. Much later, after the Thunderbolts' imposture had been revealed, the Masters attempted to recruit the remaining Thunderbolts who had decided to retain their heroic roles, threatening to turn them over to their other criminal adversaries if they refused. Ultimately, resenting these threats, the Thunderbolts unsuccessfully battled the core group of Masters.
Shortly thereafter, Hawkeye became the Thunderbolts' leader, and the team decided to capture the Masters of Evil in hopes of establishing for the public their noble intentions. Despite being confronted by the entire 25-member lineup of the sixth Masters, the Thunderbolts succeeded in defeating them all and thwarting their scheme to extort one trillion dollars from the governments of the world. Though most of the Masters were captured, Man-Killer was one of the three criminals who escaped the scene of the battle.
Van Horn adopted a cover identity as a bartender in Colorado, but she was soon discovered by the alter ego of the Thunderbolt Atlas. Atlas remained unsure whether to expose her, but at some point Man-Killer had also deduced Atlas' identity. Atlas ultimately confronted her when he was attacked by Wonder Man as part of plan formulated by Count Luchino Nefaria. Van Horn rejected his overtures of friendship and escaped, her cover blown.
Van Horn next appeared once more in the Crimson Cowl's employ. The Masters of Evil were confronted by Hawkeye and his allies Songbird and Plantman (then, Blackheath) who were searching for the legacy of Justin Hammer. Their search ended with Hammer's daughter, Justine, who turned out to be the Crimson Cowl. Hawkeye convinced van Horn and other members of the Masters of Evil to side with him against Crimson Cowl and their former allies, pointing out the dangers of the super-weapon: it was a biological toxin that had been ingested by every single villain, including van Horn, and would instantly kill them anywhere on the Earth. Hoping to throw off suspicion, Hawkeye made the villains reinvent their costumed identities, and van Horn joined his new team of Thunderbolts as Amazon.
The group ultimately defeated the Cowl and her Masters of Evil, and Blackheath managed to release an antidote into the atmosphere instead. The Thunderbolts immediately fought against the Elite Agents of SHIELD, who had caught up with them and wanted the remains of Blackheath's body, although he soon revived himself. The Thunderbolts were aided by the arrival of the true Citizen V, who needed the team's immediate help with his agency's ship.
The engines of the ship were of alien technology and had began distorting, threatening to suck the Earth into the null space of a white hole. Hawkeye's Thunderbolts were asked to move a great quantity of mass to plug the hole, and van Horn was instrumental in helping the team survive. In so doing, the Thunderbolts encountered the original Thunderbolts, who emerged from the void after severing the alien ship's presence from where they had been trapped on Counter-Earth. The two teams of Thunderbolts combined forces to plug the void and shunt the alien ship from Earth, similar to the manner in which Zemo's team stopped the threat on Counter-Earth. After much discussion, most of the costumed heroes and villains chose to part company, including van Horn, who never considered herself a hero to begin with.
As simply Katrina, she tried to break into a gem vault but was apprehended by Spider-Man. Before she could be picked up by the authorities, she was rescued by agents of Rey Trueno, who organized an underground fight club called the Unlimited Brawling Championship. Van Horn joined the club, although she remained very antagonistic to her coach and others. She briefly joined other club fighters in a “Spider-Man Revenge League,” but she dropped out of the League and the Championship before ever confronting Spider-Man again.
Instead, she was recruited by Baron Zemo and MACH-IV to form a counterpart to the new Thunderbolts. Zemo hoped to use the team to force the Thunderbolts to sacrifice the life of Photon, whose existence threatened the future of the universe. During the battle, she confronted Atlas, surprising everyone by displaying growth powers given to her by the Fixer. Although she was defeated, Zemo succeeded in killing Photon. Afterwards, Man-Killer parted company with the Thunderbolts.