In the "Quake" game series...is it ever revealed who QUAKE is?

Question

One would assume that it's the last boss (Shub Niggurath), but both her and QUAKE were mentioned in the book as separate entities. And there's no answers in "Quake 2-4" since they're based on an entirely different storyline. Is this something that was simply overlooked? Was there an answer? Or is it Shub? (please provide source if it is Shub)

QUAKE, as stated in the book, is a code name for an enemy, not the marine you play as.

Answer 1

Couldn't QUAKE be the codename for your "Space Marine" character... after all, he's referred to as "the QUAKE guy" ;);)