William Birkin is a character file that can be found in Resident Evil: The Darkside Chronicles.
William was the discoverer of the G-Virus, and also the one responsible for bringing about its fulfillment.
Once the pride of the Umbrella Corporation, he began to disagree with the company's policies and procedures while he was working on the G-Virus. It was at this time that he contacted the U.S. military to negotiate a deal.
However, although William planned to monopolize the virus for himself, his plan was thrown into disarray by an attack from Umbrella's Special Forces.
Just before his death, he injected himself with the G-Virus, which transformed him into the life form known simply as G.
Official English localization