S. Holmes

S. Holmes is a guard at the Mars City Marine Command. He was stationed there by order of Sergeant Kelly to guard the HQ. When the marine gets there, Holmes tells him that "If you don't get to the HQ, Sergeant Kelly will teach you a lesson" . Holmes was in Mars City when the Delta Labs Teleporter failed and created a gateway to hell. Holmes lost his helmet during combat. He can be found when the Doomguy arrives at Marine HQ, where he is strangled to death by a zombie.

Trivia
S. Holmes may be a reference to Sherlock Holmes. His helmet can be seen on the floor between the HQ and the Infirmary.