Nemesis

The Nemesis-T Type (also known as the "Pursuer") is the main antagonist of the titular game Resident Evil 3: Nemesis. It was named after Nemesis, the Ancient Greek goddess of divine vengeance.

Pre-Resident Evil 3
The European branch of Umbrella originally developed the Nemesis as an offshoot of the American-led Tyrant project, with the emphasis on increasing the host's intelligence and ability to follow orders without compromising the Tyrant's inherent strength and power. The breakthrough came with the creation of the NE-α Type parasite. This parasite could take control of its host's brain stem and act as a second brain replacing the host's now useless original one.

Resident Evil 3
The Umbrella Corporation deployed the Nemesis to hunt down and kill the surviving members of S.T.A.R.S. team, who had been a thorn in the corporation's side since the original Arklay Mountains outbreak with the company seeing a chance to deal with them in the chaos of the Raccoon City Destruction Incident. Nemesis claimed his first victim in the form of S.T.A.R.S. pilot Brad Vickers, chasing him to the Raccoon City Police Department where, cornering the injured man outside the front doors, the monster killed him instantly by using an extending tentacle to impale Vickers through the mouth, breaking his neck as Jill Valentine looked on in horror.

After killing Brad, the Nemesis chucks his dead body aside and advances on Jill. Depending on player choice, Jill either runs immediately into the police station or attempts to retrieve Brad's S.T.A.R.S ID card from his corpse and then head into the station. Once inside, the Nemesis is unable to get past the front doors and is kept temporarily at bay. However, after Jill contacts Carlos Olivera via a radio in the S.T.A.R.S office, the Nemesis bursts through a window and continues his pursuit. However, Jill is able to evade him and escapes the precinct.

Jill evaded Nemesis multiple times as she explored the city, each time barely escaping with her life. Having encountered Olivera and his squad and repairing the trolley car, Jill with UBCS ally Carlos Oliveira continue their perilous trek through the city, but once again Nemesis is able to catch up to them. He breaks inside the train with ease, where the injured UBCS mercenary Mikhail Victor manages to keep him occupied long enough to blow up the train car with a grenade, forfeiting his life but successfully incapacitating the monster, who is blown out of the trolley onto a burning heap on the road.

Despite managing to reach St. Michael Clock Tower in the northern part of Raccoon City, Nemesis relentlessly tracks her down inside the tower, even shooting down the rescue chopper summoned to her aid. In the burning ruins of the tower's courtyard, Jill is forced to confront Nemesis. Using the same tentacle that he used to impale Vickers, Nemesis is able to infect Jill with the t-Virus before the battle even begins. Nevertheless, she unloads on Nemesis with a barrage of heavy firepower and explosives, finally defeating the monster. Severely crippled, the Nemesis staggers towards a fire and falls in. Now with much of its coat burned off, Nemesis enters its second mutation as a host of writhing tentacles erupt from its body. This seemingly indestructible monster reappears again while Carlos is returning from a trip to a local hospital with a vaccine for Jill. Battering his way through a brick wall, and now brandishing a whole new host of tentacles erupting from its arm, it attempts to stop Carlos, who makes a beeline for Jill and is able to administer the cure. Though she manages to lose the monster for some time in Raccoon Park, she encounters Nemesis again waiting on the bridge to the Dead Factory where she eludes him by jumping into the river below. Making her way through the facility Jill is later forced to battle Nemesis for a second time in the plant's waste disposal room. Using the chemical taps located around the chamber, she is able to burn and maim the monster before dumping its horribly mutilated corpse into the plant's dissolving pool. Perhaps finally believing Nemesis to be dead for good, Jill heads for the facility power plant hoping to find a way to escape the city. Inside the plant, she finds evidence of a recent battle between United States Army Special Forces and Umbrella B.O.W.s, with a large railgun having been installed inside the chamber. At that moment the Nemesis reappears, having somehow withstood being submerged in the dissolving pool. Now little more than a quivering mound of necrotic flesh, the creature squirms over to a dead Tyrant (T-103 Model) and begins feeding upon it. This triggers a final mutation, with Nemesis becoming a huge tentacled organism which, despite having lost all vestiges of human intelligence, is even more resistant to damage and can now spit a deadly venom over large distances.

Jill quickly realizes that her only defense is the railgun, and after a series of direct hits, Nemesis finally appears to be vanquished. As Jill heads for the door, however, the creature begins to stir. Eager to be rid of it once and for all, Jill picks up a discarded magnum and empties the gun into what's left of the monster. With a shudder, the Nemesis finally dies, its organic matter slowly dissolving into nothing.

Ultimate Marvel vs Capcom 3
Nemesis is a playable character in the updated Marvel vs Capcom 3 along with fellow Resident Evil Characters: Wesker, Chris Redfield and Jill.

Nemesis' ending involves him joining the Weapon X program. Ozwell E. Spencer lauds The Director on the upgrade, although The Director merely states that they're nothing more than "minor enhancements". Nemesis is then seen with adamantium claws on his hands.

Trivia

 * Nemesis is very similar to Silent Hill's Pyramid Head.
 * Both appeared in a sequel.
 * Both relentlessly pursue the protagonist in the game they appear in.
 * Both appeared in their series' respective movies.