First appearance: Resident Evil 2
It's one thing to love your work. It's another thing entirely to inject yourself with the G-Virus to exact revenge on your bosses for trying to kill you. That's just what William Birkin did, and as you can plainly see, it didn't exactly work out for him. Changing from regular, mild-mannered scientist to an overgrown monstrosity with an eyeball for a shoulder isn't exactly an upgrade, even if you were about to die.
Seriously though, Birkin's transformation into "G" was obviously painful, and the end result is really revolting. Birkin's transformations kept happening too, with his final form turning him into a giant slug with crazy teeth and, you guessed it, tentacles. We'd feel bad for Sherry, but honestly, she's better off. It's not like grade school has a "Bring Your Father Who Turned Into a Mutated Monster With a Giant Eye-Shoulder, and Tried to Kill You to School Day."