Nemesis is a genetically-engineered super-soldier developed by the Umbrella Corporation in Paul W. S. Anderson's Resident Evil film series. This mutant monster is based on the creature of the same name from the video games, though there are significant differences between them. The Nemesis appeared in the series' second installment, Resident Evil: Apocalypse.
The Nemesis was once a human being by the name of Matt Addison, a member of an environmental group crusading against Umbrella and trying to expose the company's illegal genetic research. Matt had disguised himself as a cop and was investigating the disappearance of his sister Lisa, searching the Arklay Mansion that served as the emergency entrance to The Hive, Umbrella's secret research complex located beneath Raccoon City. Matt was handcuffed by Umbrella operatives sent to investigate the Hive after it was suddenly sealed and was taken down into the complex and kept under guard. However, he managed to free himself and helped Alice Abernathy escape the facility alive, although he was wounded by a mutated Licker in the process. The Licker's attack infected Matt with the T-virus and he started to mutate shortly after he and Alice got out. Umbrella scientists captured Matt and Alice, taking them to their facility in Raccoon City Hospital where they conducted experiments on them.
Not long after his capture, Matt became the primary test subject of Umbrella's Nemesis Program. The mutant strain of the T-virus severely warped his body and Umbrella's further experimentation turned him into a near-invulnerable engine of destruction. Equipped with cybernetic implants and heavy weapons, Matt had become Nemesis.
When the T-virus spread throughout Raccoon City, Major Timothy Cain - the man in charge of the Nemesis Program - had his new creation activated and sent out into the city to test its capabilities. Its first order was to terminate the surviving members of the Raccoon City police force who had taken shelter in a gun shop and it was later commanded to hunt down and kill Alice. Nemesis found Alice and former cop Jill Valentine and pursued them, but Alice had gained new superhuman abilities of her own after Umbrella had experimented on her and she was able to evade the creature.
Later, as Alice and her group of survivors prepared to take a helicopter at City Hall, they were interrupted by Major Cain and his troops and taken prisoner. Nemesis was recalled and Cain forced Alice to fight the monster hand-to-hand. While Nemesis was larger and stronger, Alice was faster and could think on her feet while Nemesis was subject to his programming. Alice seemed to gain the upper hand during the fight and left Nemesis impaled on a large shard of metal, but at that moment she realised that Nemesis was actually Matt, the man who had helped her escape from the Hive. Cain urged Alice to finish Nemesis but she refused, and so Cain commanded Nemesis to kill Alice before he and his troops evacuated. Nemesis picked up his weapons and took aim, only to fire on Cain's troops instead of Alice. Somehow, Matt had broken Umbrella's programming and come back to his senses.
Nemesis/Matt used the superior strength Umbrella had given him to fight off Cain's soldiers and was able to save Alice yet again by shooting down two Umbrella choppers with his rocket launcher. However, one of the choppers came crashing down right on top of Nemesis, seemingly killing him. Though it was possible that Nemesis survived the chopper crushing him, he would have died anyway when a nuclear missile detonated over Raccoon, destroying the entire city.
The film version of Nemesis is different in many ways from the one that appears in Resident Evil 3: Nemesis. For starters, its eye is green whereas the game version's eye had no colour. The game version had a parasitic tentacle that it could use to impale opponents, and while the film version of Nemesis has a tentacle-like appendage appearing around its neck, it does not move and may not be a tentacle at all.
Both versions of Nemesis were extremely strong and seemed to be immune to gunfire. They also both wielded a rocket launcher, though the film Nemesis also wielded a helicopter rail gun.