Turing's world was markedly different from the one in which we live today. In fact, much of the technology which we now take for granted can be traced back to him in some way. Ever heard of an algorithm? You can thank Alan Turing for that little gem, who originated the concept in a paper while at Kings College, Cambridge.
Best remembered for his work at Bletchley Park in wartime, Turing devised the electromechanical Bombe, which was able to find settings for the Enigma machine, enabling encrypted German messages to be deciphered - which proved to be an invaluable resouce.
After the war, Turing went on to explore the possibilities of artificial intelligence, publishing papers on the subject and creating the "Turing Test", which determined whether the responses of an artificial intelligence could be told apart from the responses of a human being.
But Alan's highly celebrated career was marred and ultimately cut short by a tragic personal life. In January 1952, Turing met a man called Arnold Murray outside a cinema in Manchester. After a lunch date, Turing invited Murray to spend the weekend with him at his house, an invitation which Murray accepted although he did not show up. The pair met again in Manchester the following Monday, when Murray agreed to accompany Turing to the latter's house. A few weeks later Murray visited Turing's house again, and apparently spent the night there.
After Murray helped an accomplice to break into his house, Turing reported the crime to the police. During the investigation, Turing acknowledged a sexual relationship with Murray. Homosexual acts were illegal in the United Kingdom at that time, and so both were charged with gross indecency under Section 11 of the Criminal Law Amendment Act 1885.
Turing was given a choice between imprisonment or probation conditional on his agreement to undergo hormonal treatment designed to reduce libido. He accepted chemical castration via injections of stilboestrol, a synthetic estrogen hormone.
Turing's conviction led to the removal of his security clearance, and barred him from continuing with his cryptographic consultancy for the Government Communications Headquarters (GCHQ), the British signals intelligence agency that had evolved from GCCS in 1946. At the time, there was acute public anxiety about spies and homosexual entrapment by Soviet agents, because of the recent exposure of the first two members of the Cambridge Five, Guy Burgess and Donald Maclean, as KGB double agents. Turing was never accused of espionage but, as with all who had worked at Bletchley Park, was prevented from discussing his war work.
Unfortunately, the fact that Turing had helped save countless lives and secure a win for the Allies during the war did not prevent him from becoming utterly ostracized by his government and peers. He was relieved of his security clearance and forbidden from continuing his work at the Government Communications Headquarters. Two years later, Alan Turing was found dead.
On 8 June 1954, Turing's cleaner found him dead; he had died the previous day. A post-mortem examination established that the cause of death was cyanide poisoning. When his body was discovered an apple lay half-eaten beside his bed, and although the apple was not tested for cyanide, it is speculated that this was the means by which a fatal dose was consumed. An inquest determined that he had committed suicide, and he was cremated at Woking Crematorium on 12 June 1954. Turing's mother argued strenuously that the ingestion was accidental, caused by her son's careless storage of laboratory chemicals. Biographer Andrew Hodges suggests that Turing may have killed himself in an ambiguous way quite deliberately, to give his mother some plausible deniability. Hodges and David Leavitt have suggested that Turing was re-enacting a scene from the 1937 film Snow White, his favourite fairy tale, both noting that (in Leavitt's words) he took "an especially keen pleasure in the scene where the Wicked Queen immerses her apple in the poisonous brew."
LGBT campaigners are still petitioning for an official pardon of Turing's indecency charges, although as yet the answer is "no", with Lord McNally defending the government's decision by stating that he was rightly prosecuted under the law of the era. But while a pardon may not be immediately forthcoming, John Graham-Cumming did at least succeed in procuring a public apology from then-Prime Minister Gordon Brown in 2009.
Brown responded by writing about Turing at length in a piece in the Telegraph, stating: "Alan deserves recognition for his contribution to humankind. For those of us born after 1945, into a Europe which is united, democratic and at peace, it is hard to imagine that our continent was once the theatre of mankind's darkest hour." Harder still to believe, as we celebrate all that is great about Britain this year with the Diamond Jubilee and Olympic Games, that a man could suffer so much at the hands of his own country, when it owed him such a debt.
The word "legacy" can be bandied around and overused from time to time, but in this instance it could not be more apt: not just for the debt of thanks we all owe to Alan Turing for his wartime work but also for the opportunity that his life story offers; the opportunity to learn from the mistakes and prejudices of the generations that came before us, and ensure that they are never repeated.
In the words of Gordon Brown: "On behalf of the British government, and all those who live freely thanks to Alan's work I am very proud to say: we're sorry, you deserved so much better."