Who was Alan Turing and what happened to him after the war?

Alan Turing was a British mathematician whose 1936 paper on computable numbers introduced the theoretical machine that underpins modern computing, and who went on to play a central role in breaking German ciphers during the Second World War.

At Bletchley Park he led Hut 8, which attacked the German naval Enigma — the hardest variant, and the one that mattered most to the Battle of the Atlantic. He designed the Bombe, an electromechanical machine that dramatically narrowed the search for daily Enigma settings, building on earlier Polish work. Historians differ on precise figures, but the consensus is that the codebreaking effort shortened the war substantially and saved a great many lives.

After the war he worked on early computer design at the National Physical Laboratory and Manchester, and in 1950 published the paper proposing what became known as the Turing test. He also did pioneering work in mathematical biology on how patterns form in nature.

In 1952 he reported a burglary to the police and, in the course of the investigation, acknowledged a relationship with another man. Homosexual acts were criminal in Britain at the time. He was convicted of gross indecency and, to avoid prison, accepted hormone treatment intended to suppress his libido. He lost his security clearance and with it his work on government cryptography.

He died in 1954, aged forty-one, from cyanide poisoning. The inquest recorded suicide; some later researchers have argued accidental inhalation from his home chemistry experiments is also consistent with the evidence.

He received a formal government apology in 2009, a royal pardon in 2013, and appears on the Bank of England's £50 note.