Yeah, I know, most people are thinking, “Who?” To me he was the R in K&R, but that probably doesn’t clue many people in either.
Basically, co-creator of the C programming language and key designer in the early days of Unix which puts him at ground zero when it comes to modern operating systems. Sure, they’re not all written in C these days, but at the core they are. BSD, Linux, OS X, and the Windows NT kernel are all C based for the most part.