Alan Turing (23 June 1912 – 7 June 1954) was a British mathematician who contributed hugely to modern computer science and cryptography. Though perhaps not the father of computer science, he " is frequently credited for being the father of theoretical computer science and artificial intelligence."
The Turing Machine
In the 1930s Turing proposed the concept of a "Universal Turing Machine". Turing had, first, proposed that the operations needed to calculate any formula could be broken down into a base set of instructions (or primitive recursive functions) that could in principle be followed by a machine: the "Turing Machine". Once fully formalized the calculations needed to derive the instructions themselves were capable of being run by a Turing Machine. The looped logic allowed the conception of a Turing Machine that could create its own instruction and, in principle, run a huge variety of calculations. Turing then used the concept of Universal Turing Machine to prove the undecidability of the halting problem.
During World War II Turing was assigned to the codebreaking unit at Bletchley Park, where he worked on the decoding of the German's Enigma machine. Turing and his colleagues played a significant role in the Allied victory in WW2, allowing Allied forces access to German communication networks throughout much of the war.
In his 1950 paper "Computing Machinery and Intelligence" (Mind 49: 433-460) Turing proposed a test (apparently heavily influenced by Logical Positivism) for establishing whether a computer could think (see artificial intelligence). This test, the turing test, is still widely considered to be the best test of whether a machine exhibits artificial intelligence.
Turing committed suicide by eating a poisoned apple after he was forced to take hormone treatment as part of his punishment for being convicted of homosexual acts. On September 10, 2009, British Prime Minister Gordon Brown issued a statement to "celebrate" Turing's "contribution to Britain’s fight against the darkness of dictatorship" and to acknowledge that his prosecution was "appalling" and "utterly unfair". "I am pleased," Brown stated, "to have the chance to say how deeply sorry I and we all are for what happened to him."
Online biography: http://www.turing.org.uk/bio/
Computing Machinery and Intelligence: http://cogprints.org/499/00/turing.html
Oddballs and Eccentrics. Shaw, Karl. Edison, New Jersey: Castle Books, 2004.