Master Sergeant Kelly who plays a main role in "Doom 3", has a cameo in this game where you find a picture of him in Erebus Level 3 on a wall, just as you grab the double-barrel shotgun. See more
[to the Marine
What did you hope to accomplish by coming here, mortal?
[referring to the Artifact
You have something that belongs to me, and I want it.
[flies off and attacks the Marine