T-001 (otherwise known as the Proto Tyrant) was the result of experiments by Umbrella into the creation of super soldiers. Although it was not considered a success due to it's many disadvantages, it served as the basis for all the future Tyrant models created.
It was created by increasing the dose of a
t-Virus infection to dangerous levels which caused some unique effects such as an exposed circulatory system with a massively enlarged heart, paper-thin skin which tore with relative ease, and an exposed spine. On the plus side, the monster was hulking and powerful with a super-deformed right arm with spikes of different lengths.
The creature itself had many other interesting physical characteristics such as some exposed bone, an enlarged mouth and glowing white eyes. It also had sections of it's upper body with much thicker, darkened skin - particularly on it's spiked arm.
However, it's many disadvantages made it unsuitable to be considered a success, as it was relatively weak due to it's heart and spine serving as critical injury points. Thus, Umbrella moved the Proto Tyrant to their NEST Facility by holding it in a storage tank awaiting disposal.
At some point the creature was released from containment and took on Dr
Albert Wesker,
Rebecca Chambers and
Billy Coen at separate occasions and was eventually incapacitated and later destroyed when the facility was destroyed via a self-destruct mechanism triggered by Dr
William Birkin. The Tyrant did not mutate further when healing unlike future versions, it's highly likely that the initial form was the only form it could take.
Despite everything, Umbrellas research was complete and they used what they had learned to improve upon the groundwork set and eventually developed more advanced Tyrant models.