Pluto was the designation given to a failed experiment by Umbrella - in theory, it was supposed to be a super-powered B.O.W. (Bio-Organic Weapon) similar to a Tyrant. The monsters biological base was a human male who was reportedly a petty criminal, and the monster was created gradually through horrific scientific methods. How they obtained the specimen is unknown, but it's likely that they were pressured into joining Umbrella in exchange for freedom, under false pretences.
After initial viral infection, the subject began to transform into a hulking, indestructible beast. Due to great pain being caused to it from the experiments, their frontal lobe was punctured by a metal rod. This destroyed their speech centre as well as any kind of conscious reasoning - this was either done to help it or to simply silence it. However due to the haphazard nature of how the rod was inserted, it left a hole in their skull which would later become it's only weak point.
Some time later, Umbrella scientists decided to remove both of its eyes just to see if any of the other senses would take over and be enhanced - it also had the other side effect of them potentially being able to control creature, with it now being unable to use sight as a decider on how to act. Eventually, the creature developed superhuman hearing.
It's body continually developed body mass, but this was being stored as fat rather than muscle as expected. To combat this, the scientists saturated the Pluto with steroids. While this did increase muscle density and promoted development, it also increased its aggression markedly which made it impossible to control. The fully developed creature resembled a large, fat human with many 'rolls' of bloated flesh around its body. It had a highly mutated left arm that had long tentacles in place of digits which appeared to look similar to what the
T-091 Tyrant had, albeit only on one side.
After this, Umbrella decided that the project was a failure and ordered it to be disposed at an island facility. It remained there in a special chamber until it was awakened and went on a rampage, killing many. He was later encountered by
Bruce McGivern and defeated relatively quickly. As it had an exposed brain, Bruce took advantage of this. Additionally, the fact that it could only rely on sound, Bruce remained slow and silent and opted to use a Silenced handgun to attack it. Otherwise, he would have been impossible to defeat.
In some media the Pluto is referred to as a type of Tyrant, although it was a separate project and it didn't use any of the
T-103 Tyrants as a base. Rather, it seems to be a unique monster built a different way.
