Tremendously influential in the creation of computer science, supplying a formalisation of the notions of “algorithm” and “computation” with the Turing machine, which is often considered a model of a general purpose computer, Alan Turing is broadly regarded as the father of artificial intelligence and theoretical computer science.
For a time he directed Hut 8, the department responsible for German naval cryptanalysis. He formulated several techniques for breaking German ciphers, including progress to the prewar Polish bombe system, an electromechanical machine that could uncover settings for the Enigma machine. Turing’s critical function in deciphering intercepted coded messages enabled the Allies to defeat the Nazis in several critical battles, for example, Battle of the Atlantic; it was estimated that the war shortened in Europe by as many as two to four years.
The Turing Digital Archive: http://www.turingarchive.org/
Alan Turing on Wikipedia: http://en.wikipedia.org/wiki/Alan_Turing
Alan Turing on BBC History: http://www.bbc.co.uk/history/people/alan_turing