Alan Turing
Alan Turing was a British mathematician, computer pioneer and computer scientist. He has been called "the father of computer science". A fine biography is "Alan Turing: the enigma" by Andrew Hodges [1].
He made large theoretical contributions to computer science in the 1930's, before any actual computers were built. He invented the Turing Machine, a mathematical model of a computing system that is still widely used, and used it to solve the halting problem, the computer science analog of Godel's Incompleteness Theorem.
During the Second world War, Turing was one of the key codebreakers on the British ULTRA project which read many German codes throughout the war.
After the war, Turing was involved in building one of the world's first digital computers at Manchester University. He also continued theoretical work and, in a 1950 paper titled "Computing Machinery and Intelligence" [2], he was among the first to ask "Can machines think?" As a partial answer, he proposed the Turing test for successful artificial intelligence. If a skeptic cannot distinguish a computer from a human by having a conversation with it, then he must admit the computer behaves intelligently.
Turing was homosexual and, after the war was prosecuted for this and forced to undergo hormonal "therapy" for this "condition".
Turing died of poison, apparently suicide, in 1954.
Turing is commemorated in several ways: