Jonathan Ishii

Jonathan Ishii was a scientist on the Delta Science Team. He went missing shortly before the demon invasion. Nobody would have known where he was heading if he was not seen in Mars City Underground approaching the airlock that led to the old communications array. Concerned that he was injured and unable to respond to pages or return to his post, Sergeant Kelly sent Doomguy out to find Ishii. Upon finding Ishii, Ishii cryptically told Doomguy "The devil is real..I know, I built his cage." Right after saying that, the demon invasion began and Ishii became a zombie, which was quickly dispatched by Doomguy.

It is also possible to kill Ishii before he becomes a zombie.