Dr. William Birkin was assigned to work on the G-Virus project.
During September 1998 he was infected with the G-Virus and mutated, the reason of the infection is unknown[note 1]
In the story, he is encountered by Elza Walker in the factory where he makes his appearance by calling for his daughter, "Sherry" and he is also fought by Leon S. Kennedy in the Underground Labs. He attacks the duo numerous times in the lab and is confronted for the last time in the Umbrella Train.
One of the most familiar and iconic frames from the past, and a well known Biohazard 1.5 footage. In the Footage, Birkin says "Sherry!", the only time he had ever been known to talk. Since 1.5 was scrapped, he hadn't been heard speaking canonically, till the remake of Resident Evil 2.