This where it all began, with the S.T.A.R.S. Alpha Team sent to investigate the disappearance of the Bravo team. They come under attack and seek refuge in Spencer Mansion, which they discover is an Umbrella research facility set up to develop the T-Virus as a biological weapon. Chris Redfield and Jill Valentine save the day, defeating the Tyrant - the ultimate biological weapon - and survive the incident along with Barry Burton and Rebecca Chambers. Alpha team leader Albert Wesker turns out to be an Umbrella employee ordered to lead the operatives to their doom in order to collect combat data.
Links in the chain
The T-Virus was developed at Spencer Mansion under the supervision of Umbrella President Ozwell Spencer. Not much is known about his character, despite his importance to the whole series.
The case of Lisa Trevor only appears in the RE remake (2002). Daughter of Spencer Mansion architect George, she was kidnapped and experimented on by Dr. William Birkin and Albert Wesker, and appears as a tough, grotesquely mutated monster.
In RE: Dead Aim, Umbrella fires Morpheus D. Duvall, accusing him of causing the leak of the T-Virus that led to the Spencer Mansion incident. In revenge, he steals the TG Virus from them.