Marcus Caseon

Marcus T. Caseon was a doctor who worked at Mars City. One night, a patient came to him complaining of insomnia. Marcus then went to get the right medicine for the patient. When he came back twenty minutes later, the patient had become incredibly hostile and angry, had self-mutilated by cutting his own tongue into two halves, and attacked Marcus with a scalpel. Marcus survived the attack. Shortly afterward, he requested to leave Mars. His request was granted. He was scheduled to leave shortly before the demonic invasion occurred, on the same ship (the Darkstar) that delivered Counselor Swann, Jack Campbell, and the marine to Mars. Before leaving, he encounters the marine. Marcus, still disturbed from his patient's attack, warns the marine not to trust anyone on the base, and that strange activities have been taking place in Mars City.

Marcus may be one of the few characters besides the protagonist to survive the events of Doom 3, as he may have been able to board the Darkstar before the invasion. This remains unconfirmed, however.

His PDA can be found in the infirmary the second time the player visits Mars City. The PDA contains the code for a supply cabinet.