Going by the name Doom:
Once, Crash was Doom's military instructor.
Long after everyone else on Phobos was dead (the only other survivor came to be known as Phobos (character)), he kept fighting, determined to send out a warning to Earth before the demons could claim him.
Distracted and intelligent sounding, (but not a member of the intelligentsia, more like a well-educated tradesman) this guy may be a few cards short of a full deck, but his training serves him well. He's a bad-ass in the arenas.
In Quake Champions "Doom" is established to be the Doom Slayer, and the uniform appears as one of Doom Slayer's alternate armor sets. The armor lore appears to set it apart as being another point in Doom Slayer's (originally Doom Marine's) history, and another mission to Phobos than occurred in Doom 1. The original Doom 1, 2, Final Doom, and Doom 64 armor appears as a seperate armor set.