>Doomguy, "traumatized"

Specifically?

A constant juvenile humor to distract his mind (fist bumping bobble heads, doing Terminator 2 references even while BURNING TO DEATH IN LAVA), mixed with a quiet a complete contempt for the idiots in charge that keep on fucking with demons, a single minded dedication to murdering demons as violently as possible (and treating them as less than garbage once they die, as mere trash to throw away), and finally the satisfaction knowing that demons all are scared shitless of him and view him as their boogie man.