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"Another replacement, huh?"
― Miller upon greeting the player  [src]
"Another newbie, welcome to the worst assignment you will ever have!"
― Marak upon greeting the player  [src]

K. Miller and M. Marak are minor characters in Doom 3. They are both Marines stationed on Mars.

The player will encounter them off-duty in the Mars City Common Area, talking about a member of Bravo Team, Corporal Allen, who was recently shipped back to Earth due to psychological problems. Wondering who the new replacement will be and hoping it does not put them into extra shifts, their questions have been answered when the player arrives to speak to them, which they respond with a couple of cold-hearted greetings.

It's likely during the demonic invasion, they set up a defense in the cafeteria but were likely killed given the amount of blood the area is splattered with.