Dennis Ritchie?! Who is Dennis Ritchie? Will be the first tought of many.
Dennis Ritchie is the inventor of the computer programming language C. In my eyes he has done even more work for the world than Steve Jobs did. (Sure he had a good eye for how things should look.)
Next to his job for creating the programming language C he was also known as one of the key-developers for UNIX. From those two positions he has had quite some influence on how todays Operating Systems look like and function.
Wired News: Dennis Ritchie: The Shoulders Steve Jobs Stood On
Los Angeles Times: Dennis Ritchie dies at 70; computer scientist helped develop Unix
New York Times: Dennis Ritchie, Trailblazer in Digital Era, Dies at 70