Proto Tyrant (T-001 Model) was an experimental subject which served as the prototype for the later Tyrants. Despite its primitive design in comparison to later B.O.W.s, it nonetheless demonstrated the "bare ferocity" that earned its series the name "Tyrant".[excerpt 1]
Aimed at developing the "ultimate life form", the T-001 was developed alongside the "finished product", T-002. During the experiment, the t-Virus' negative effects were found to be too potent, resulting in such deformities as the skin essentially "exfoliating". This led to the decision to discontinue the Tyrant's development.
While the T-001 was scheduled to be destroyed, it was released during the incident in the Arklay Mountains when the Raccoon City Underground Laboratory became infested. Shortly thereafter, it met S.T.A.R.S. officer Rebecca Chambers during the events of July 24th in the B4F turntable room, and while classified as a failure, it was nonetheless a powerful opponent. Rebecca managed to defeat it after a long battle, and then resumed her search for Billy Coen. However, its "t" regenerative capabilities were underestimated, and the Tyrant broke through the emergency shutter and confronted Rebecca and Billy a final time in the water treatment plant. They managed to fight off the beast and defeated it again.
After a short while, the Tyrant quickly regenerated and managed to reach the Marshaling Yard above the underground laboratory through the train elevator during a fight with Albert Wesker, shortly after Rebecca abandoned it. Its regenerative capabilities helped it recover, and it attacked Wesker again before finally being killed for good.