The Pluto was one of Umbrella's failed bioweapons experiments. It shares its name with the Roman god of the underworld. Rather than most B.O.W.s, Pluto was a mutant human, a man only identified as "α".
Originally a man imprisoned for a capital offence, Umbrella was able to get him to participate in what he believed to be a pharmaceutical trial. Taken to a facility on an island in the Atlantic Ocean, he was kept him in containment for a month before initiating the experiment, leaving him distressed. On Thursday, September 26th, 1996, his doctors began by hammering a metal rod into his frontal lobe to prevent him being able to feel pain, which they considered necessary for humanitarian reasons. On September 29th, his eyes were surgically removed to take part in research on how it would effect his senses. On October 9th, he was injected with experimental steroids to assess the growth of muscles, which quickly expanded disproportionately. On October 31st, his body finally responded to the loss of eyesight by developing increased hearing, allowing him to track his doctors' movements. On the November 5th, Pluto made his escape with the use of his new abilities, killing five guards in the process.
Due to serious failings in safety standards starting from Morpheus D. Duvall, Pluto was never captured by the Umbrella Security Service or by workers, and was left to roam the facility for several years. By 2002, the facility had been abandoned by Umbrella HQ and occupied by terrorists. USSTRATCOM agent Bruce McGivern made his way to the facility, and killed Pluto in a storage room.