The basic Doom 3 Zombie is a reinterpretation of the classic Former Human. They were once UAC civilians, now possessed by evil spirits. A scripted event early in the game shows scientist Jonathan Ishii coming into contact with a transparent "ghost skull", which turns him into a Zombie. The demonic force that creates Zombies does not differentiate between the living and the dead - slain humans will be re-animated as Zombies, and do not seem to be any less powerful than the ones created through possession of a living host. They stop appearing after the marine returns from Hell.