William Birkin is the secondary antagonist of Resident Evil: Undead. He was an Umbrella Corporation Executive and one of the people responsible for the outbreak as well as Albert Wesker's best friend. He was the developer of the G-Virus and is the husband of Annette Birkin and father of Sherry Birkin. He joined Albert Wesker's group as it's second in command. His weapon of choice is a Beretta 92FS Brigadier.