I don't know what Carmack did in the business world, but he was little more than a teenager when he created the first 1st person, 3D shooter (Wolfenstein ). That was freakin fantastic at the time. Everything before that, that I remember, was 2D scrollers of one sort or another (Dragon's Lair was phony 3D). Not only did he pull that off first, he did it with a 286 computer. That's scarey impressive. That's what's so excellent about him. He followed that up with Doom (I'm skipping Spear of Destiny since it was pretty much like Wolfenstein). Each game had a generous trial version. Later Carmack made the 3D engine public, with tools for people to create their own levels. I suppose most people know that, but I don't know if most here were around and playing games when it happened. He set a fantastic precedent, and I respect the guy for a massive brain and the willingness to try to get the genre going full speed.