[livrem]

I am not sure I would consider much of what he did very simple (or easy) compared to what most of us are doing today. The last few chapters of Michael Abrash's Black Book is about his work with Quake (he was involved doing some of the graphics code together with Carmack) and it is pretty hardcore low-level advanced things they were doing. Remember they were software rendering everything in the first version.

https://github.com/neonkingfr/AbrashBlackBook

And also they did pretty soon support MSDOS, Windows 95, and Linux (and possibly some more platforms?). In addition to supporting software rendering, 3Dfx, OpenGL, and possibly some more 3D API.

[hypercube33]

Didn't he code on Solaris or something weird in the workstation family and port quake over to dos? I only remember him having a giant CRT monitor where he'd sit and code for photos back in the 90s

[Narishma]

It was NextSTEP and that was for Doom. I think they switched to Windows NT for Quake (or was that Quake 2?), which is what he was working on in that pic with the giant CRT.

[mepian]

The switch to Windows NT happened with Quake 2, the original Quake was still NeXTSTEP.