Alan Mathison Turing (1912-1954), a British mathematician and cryptographer, is considered to be one of the founders of modern computer science. He developed what became known as the Turing machine in 1936, an abstract representation of a computing device. The Turing machine is still widely used in theoretical computer science today, especially in complexity theory and the theory of computation. He formulated the now widely accepted 'Turing' version of the Church-Turing thesis, namely that any practical computing model has either the equivalent or a subset of the capabilities of a Turing machine.
During World War II, he was the director of the Naval Enigma Hut at Bletchley Park where he played a major role in cracking Nazi ciphers. After the war, he designed one of the earliest electronic programmable digital computers at the National Physical Laboratory and the University of Manchester.