Musk actually has credited Carmack's Armadillo Aerospace with providing the inspiration for vertically landing the Falcon 9. Of course Armadillo was likewise inspired by the Delta Clipper, which was in turn inspired by the LEM, etc. But it's one thing to vertically-land a rocket a few times when you have billions of dollars at your disposal; it's another thing to do it hundreds of times for a thousandth the price. That was Carmack's contribution: proving that vertical landing can be both incredibly robust, and cheap as chips. Really valuable work.

I had the pleasure of meeting Carmack a few times over the years at small aerospace conferences. He's both as true a geek and as much of a gentleman as you might imagine. I'm really looking forward to seeing what he does with AGI.