Shaun Wylie (17 January 1913 – 2 October 2009) was a British mathematician and World War II codebreaker. Early life Wylie was born in Oxford, England. The fourth son of Sir Francis Wylie (later the first Warden of Rhodes House, Oxford) and his wife Kathleen (formerly Kelly), he was educated at the Dragon School (in Oxford) and then Winchester College. He won a scholarship to New College, Oxford where he studied mathematics and classics. In 1934, he went to study topology at Princeton University, obtaining a PhD in 1937 with Solomon Lefschetz as his supervisor. At Princeton he met fellow English mathematician Alan Turing. He became a fellow of Trinity Hall, Cambridge in 1938/1939. World War II codebreaking During World War II, Turing had been recruited to work at Bletchley Park, Britain's codebreaking centre. Turing wrote to Wylie around December 1940, who was by then teaching at Wellington College, inviting him to work at Bletchley Park. He accepted, and arrived in February 1941. He joined Turing's section, Hut 8, which was working on solving the Enigma machine as used by the Kriegsmarine. He became head of the crib subsection, and allocated time on the bombe codebreaking machines. Hugh Alexander, successor to Turing as head of Hut 8, commented that "except for Turing, no-one made a bigger contribution to the success of Hut 8 than Shaun Wylie; he was astonishingly quick and resourceful and contributed to theory and practice in a number of different directions". Wylie transferred in Autumn 1943 to work on "Tunny", a German teleprinter cipher. He married Odette Murray, a WREN in the section. In 1945, soon after the victory in Europe, Wylie demonstrated how Colossus – electronic machines used to help solve Tunny – could have been used unmodified to break the Tunny "motor wheels", a task which had been previously done by hand. While at Bletchley Park, he became president of the dramatic club. He had also played international hockey for Scotland, but according to fellow codebreaker I. J. Good, he "never mentioned any of his successes". Post-war After the war, he was a fellow at Trinity Hall until 1958 and lectured in mathematics. He was the PhD advisor for Frank Adams, Max Kelly, Crispin Nash-Williams, William Tutte and Christopher Zeeman. With Peter Hilton, he authored Homology Theory: An Introduction to Algebraic Topology, published in 1960. In 1958, he became Chief Mathematician at GCHQ, the UK