UNIX creators Ken Thompson (Left) and Dennis Ritchie (Right)
In 1969, while at Bell Labs, Thompson and Dennis Ritchie were the principal creators of the Unix operating system. Thompson also wrote the B programming language, a precursor to Dennis Ritchie's "C", one of the world's most commonly used programming languages. Later, while still at Bell Labs, he and Rob Pike were the principle creators of the Plan9 operating system.
He also wrote programs for generating the complete enumeration of chess endings, for all 4, 5, and currently 6-piece endings. Using these, a chess-playing computer program can play perfectly once a position stored in them is reached.