Alan Turing was one of the three people most critical to the development of the modern electronic computer. John von Neumann defined the essential logical components - processor, memory, storage, program, and data and demonstrated the fact that such a device could perform any mathematical or linguistic operation. Turing defined core concepts such as algorithm and computation with the precision necessary to develop logic circuits and computer programs. He also coined the term "artificial intelligence" and defined the Turing Test, a test to see if a computer had acheived a certain level of human-like intelligence related to conversation.
The computer was an outgrowth of code-breaking efforts during World War II. Turing was of central importance in the successful efforts to crack the German Enigma coding machine and intercept and interpret German naval commands. This was a very important part of winning the war.
He also contributed to genetic theory, showing how the mathematical Fibonacci series expresses itself through genes into the shape of the body.
In 1952, homosexuality was still illegal in England, and Turing was convicted, then chose chemical castration over imprisonment. This largely ended his career, as the conviction carried with it the termination of his security clearance. He died of cyanide poisoning that may have been accidental, or may have been suicide. In any case, a brilliant and patriotic life was cut short by prejudice. In 2009, the Prime Minister of England issues a formal apology for the treatment of Turing regarding his homosexuality, and a pardon is currently under consideration.
You can learn more at: http://en.wikipedia.org/wiki/Alan_turing