Wartime hero, godfather of computing and gay icon - the remarkable life and tragic death of Alan Turing is marked with events around the country.
Tens of thousands of people have signed a petition to grant an official pardon for Alan Turing as events take place around the country to mark the centenary of the computer genius's birth.
Turing, considered the father of modern computing, apparently killed himself with cyanide after he was convicted of gross indecency with another man in the 1950s, when homosexual acts were still illegal.
A campaign on the government's e-petition website calling for Turing to be given a posthumous pardon has attracted more than 30,000 signatories.
Turing is best known today for his part in breaking the German Enigma code while working as a cryptoanalyst at the Bletchley Park codebreaking centre during World War Two.
Saturday's Google homepage features an animated representation of an Enigma decoding machine in Turing's honour.
Turing had already established a reputation as a maths genius by the time he was recruited as a codebreaker.
During his time at King's College, Cambridge, he devised the "Turing Machine", a mathematical model that went on to become one of the cornerstones of computer science, when aged just 22.
He was found guilty of gross indecency in 1952, and to avoid a prison sentence, he agreed to receive injections of the female hormone oestrogen in a process known as "chemical castration".
In the Second World War he saved the nation. Prof Jack Copeland
He was found dead from cyanide poisoning at the age of 41 in 1954 and the inquest recorded a verdict of suicide.
But Turing expert Professor Jack Copeland has called for the inquest to be reopened, saying important evidence was overlooked at the time and the mathematician could have died accidentally.
Prof Copeland said: "It would be a terrific thing to do. I think the nation owes it to Turing, in the Second World War he saved the nation."
The e-petition campaign says Turing's criminal conviction "remains a shame on the UK government and UK history".
It goes on: "A pardon can go to some way to healing this damage. It may act as an apology to many of the other gay men, not as well known as Alan Turing, who were subjected to these laws."
Turing's newfound status as a symbol in the struggle for equal rights was cemented on Saturday, when the British Embassy in Berlin leant a London double decker bus with a picture of Turing to the Christopher Street Day gay pride parade.
His name has been trending worldwide on Twitter, with Sarah Brown, wife of former prime minister Gordon Brown, writing: "Happy 100th Birthday Alan Turing."
In 2009, Mr Brown issued an apology for the treatment of Turing, saying: "The debt of gratitude he is owed makes it all the more horrifying, therefore, that he was treated so inhumanely."
On Saturday scientists and other Turing aficionados gathered in Manchester, Oxford and Cambridge to celebrate his work as part of Alan Turing Year.
A spokeswoman for the event said: "Turing was godfather of computer science and (an) artificial intelligence pioneer, as well as someone who saved literally millions of lives through his codebreaking work."
Dr James Grime, from Cambridge University's Millennium Maths Project, who regularly tours schools with an original Enigma machine, said: "In its purest form, mathematics is the search for truth, and Turing was one of the most important contributors to this search. It's fantastic that his life is being celebrated."
Former chess prodigy and world champion Garry Kasparov is due to attend Manchester's Alan Turing Centenary Conference on Monday.