In 1954, Alan Turing, the mathematician whose codebreaking at Bletchley Park helped the Allies read German naval Enigma traffic, was found dead at his home in Wilmslow, Cheshire, at the age of 41. An inquest ruled that he had taken his own life with cyanide. Two years earlier he had been convicted of gross indecency for a relationship with a man and forced to undergo hormone treatment. His death cut short the career of a thinker who had defined the theoretical basis of the modern computer and asked whether machines could think.
Turing's reputation among specialists rested on a 1936 paper, "On Computable Numbers," which described an abstract device, now called the Turing machine, that could carry out any calculation expressible as a set of rules. During the Second World War he led Hut 8 at Bletchley Park, attacking the German navy's Enigma cipher, and designed the electromechanical Bombe used to search for daily key settings. After the war he drew up plans for the Automatic Computing Engine at the National Physical Laboratory, then moved to the University of Manchester, where he worked on one of the world's first stored-program computers. In 1950 he proposed what he called the imitation game, a test of whether a machine's conversation could be told apart from a human's.
In 1952, after reporting a burglary at his home, Turing told police about his relationship with a young man. He was prosecuted for gross indecency, then a crime in Britain, and chose a year of estrogen injections over prison. The conviction cost him his security clearance and his consulting work for GCHQ, the successor to Bletchley Park. He kept working, turning to the mathematics of biological growth, and the patterns on animal skins and the arrangement of leaves.
His housekeeper found him in bed. Beside him lay a half-eaten apple, which was never tested for poison, and the post-mortem found cyanide poisoning. The coroner recorded suicide, though his mother insisted he had accidentally inhaled fumes from the chemistry experiments he ran in a spare room, and some biographers have kept that possibility open. Much of his wartime work stayed secret for decades. In 2009 Prime Minister Gordon Brown issued a public apology for his treatment, Queen Elizabeth II granted him a posthumous pardon in 2013, and in 2021 his portrait appeared on the Bank of England's £50 note.