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.
After a short while, the Tyrant quickly regenerated and broke through the emergency shutter. It managed to reach the Marshaling Yard above the underground laboratory via 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 being defeated. However, its "t" regenerative capabilities were again underestimated, and the Tyrant confronted Rebecca and Billy a final time in the water treatment plant. They managed to fight off the beast and defeat it again.