Jonathan Ishii

From Doom Wiki

Jonathan Ishii is a character in Doom 3. A scientist within the Delta Science Team, he disappears shortly before the demon invasion. The first assignment within the game is to find Ishii. Sergeant Kelly dispatches the player, following reports that Ishii was spotted in the Mars City underground approaching the airlock that leads to the old communications array. Upon finding Ishii, Ishii cryptically says, "The devil is real...I know, I built his cage". With these words, the demon invasion of the Mars base begins. Ishii is possessed by one of the ethereal spirits coming from the portal (as are many other humans throughout the base) and he becomes a zombie as a result. Ishii is therefore the first enemy to confront the player.

It is also possible to kill Ishii before he is possessed.