Marcus Caseon

Marcus Caseon is a character in Doom 3. He is a doctor in Mars City. One night, a patient came to him complaining of insomnia. Marcus then went to get the right medicine for the patient. He came back to the man twenty minutes later. The man had become incredibly hostile and angry and attacked Marcus, who did not know that he was not simply being incredibly hostile, he had transformed into a zombie. Shortly afterward, Marcus requests to leave Mars City, and it is granted. He leaves shortly before the Demon Invasion occurs, on the same ship that Councilor Swann, Jack Campbell, and Doomguy use to get to Mars. Before leaving, he encounters Doomguy. Marcus, still disturbed from his patient's attack, warns Doomguy not to trust anyone on the base, and that strange activities take place in Mars City.

Marcus is one of the few characters to survive Doom 3.