His record speaks for itself. I know it is tough to imagine what it was like programming 3D engines meant to run on graphics non-accelerated PCs running DOS, without the internet knowledge or collaboration available to us now, but the stuff he was doing was absolutely revolutionary. He basically created PC gaming as we know it today by creating a market for 3D accelerators and before that by doing it in software very well. He also did this stuff in an record amount of time. From Wolfenstein 3D (1992) to Quake (1995) he made three separate engines which each revolutionized the industry one after the other.
EDIT: The metric I am using is 'impact' in an industry and in society in general -- the impact of Doom and Quake on culture and the adoption of computers and PC gaming and many other things can not be overstated. You can draw a direct line from Doom to Quake to nVidia to CUDA and machine learning if you want.