Originally known in the roleplaying world as the creator or co-creator of classic games like "CallOfCthulhu" and Runequest.  Sandy Petersen began computer game design with Microprose, and in 1993 he moved to ID Software, where he was a designer on "Doom", "Doom 2", and "Quake".  He is currently a Game Designer at Ensemble Studios.

''I saw GregCostikyan speak a few weeks ago, and he mentioned that Sandy is a practicing Mormon. I have no idea how to reconcile a game like CoC with Mormonism, but then, NeilLaBute is a Mormon, too, so that makes SandyPetersen the second creatively brilliant Mormon I'm aware of ... -- francis''

Don't forget Orson Scott Card (at least I think he's a Mormon).