Dennis Ritchie
At Bell Labs in the early 1970s, Dennis Ritchie created the C programming language and, with Ken Thompson, co-created the Unix operating system. C paired low-level efficiency with portability, and rewriting Unix in C — rather than machine-specific assembly — was a radical idea that let an operating system move from one kind of computer to another.
Nearly every operating system and programming language in use today descends from that work. The book Ritchie co-wrote with Brian Kernighan, 'The C Programming Language' — universally known as K&R — taught generations of programmers and set the template for how technical books are written.
Ritchie and Thompson shared the 1983 Turing Award, computing's highest honor, for their work on Unix. He died in 2011.