Ken Thompson
Ken Thompson co-created the Unix operating system with Dennis Ritchie at Bell Labs and designed the B language, the direct ancestor of C. He wrote much of early Unix and the tools that shaped it, and shared the 1983 Turing Award with Ritchie.
In his 1984 Turing Award lecture, 'Reflections on Trusting Trust,' he described an unsettling attack: a C compiler rigged to silently insert a backdoor into the login program, and to plant the backdoor-inserting code into future versions of the compiler itself — so the malicious behavior would persist even when every line of source code looked clean. His lesson was that you cannot fully trust software you did not build yourself, all the way down.
Long after Unix, he co-designed the UTF-8 text encoding with Rob Pike — the scheme that made Unicode practical across the web — and co-created the Go programming language at Google.