Of course, the in-game version was considerably less-cool, but Mueller's art is still great.
I came across this awesome Quake III DOOM guy concept piece by Mueller, and I just freaking love it.
http://www.planetquake3.net/pic.php3?c= ... /doom2.jpg
It captures the raw DOOM II gameplay feeling, and also just sets up this awesome feeling of, "Hey, this is deathmatch -- I'm so ready to rock." Notice the instantly recognizable Quake-related symbols tatooed on his arm.

So, I'm looking for more of his Quake III work. If he's the guy that created the concept what Tankjr would look like, for instance, I'd love to see what that looks like... or Keel, or anything, really.
I've searched some, but I can't find anymore of Mueller's Quake III stuff -- just his comic book and some other conceptual stuff. If anybody knows a cache of his Quake work, I'd be more than interested in checking it out.