Ritchie is credited with creating the programming language C, one of the most widely used and influential languages today. He was also one of the creators of operating system UNIX, whose variants -- most notably Linux and OS X -- are also widely used today.
Ritchie, often referenced as dmr (a part of his email address that he used in various technical discussion groups), has had an immense influence on the computing world. Among his many accomplishments is a Turing award that he received in 1983 (together with Ken Thompson) for his work on UNIX, and the National Medal of Technology, which he received in 1999 (again, jointly with Thompson).
Programmers will perhaps best remember Ritchie for his famous “hello, world” program, which is used in many programming textbooks, even those that don’t pertain to C, as an example of a very simple computer program.
via BBC