What was Alan Turing's role at Bletchley Park?

Alan Turing's role at Bletchley Park was that of a cryptanalyst. He joined Britain's wartime codebreaking effort in September 1939 and worked in Hut 8, the section responsible for attacking German naval Enigma messages.

Turing applied mathematics, logic, and practical codebreaking methods to identify patterns in intercepted ciphertext. His most famous contribution was the design of the bombe, an electromechanical machine that tested possible Enigma settings and greatly accelerated the search for daily keys.

Calling Turing a mathematician is also factually true, but it does not best answer this question about his wartime role. He was not a spy, and “engineer” describes some technical aspects of his work less precisely than “cryptanalyst.” His work was part of a large team that included linguists, chess players, mathematicians, engineers, and other codebreakers.