The idea that starts it all
In 1936, at just 24 years old, Turing published a paper defining what "computing" means before a single computer existed: the Turing machine, a theoretical model capable of executing any imaginable algorithm. That abstract idea is, quite literally, the foundation upon which all modern computing is built.
World War II
At Bletchley Park, he led the team that designed the Bombe, an electromechanical machine capable of deciphering messages encrypted by Enigma, the system used by the German navy. Historians estimate that breaking Enigma shortened the war in Europe by several years and saved a very high number of lives. It was, in practice, the first major triumph of computing applied to a real and urgent problem.
A tragic death
In 1952, Turing was prosecuted for gross indecency—homosexuality was a crime in the UK at the time—and sentenced to chemical castration as an alternative to prison. He lost his security clearance and was barred from the work that had given his life meaning. In June 1954, he was found dead in his home; a bitten apple lay beside him. The official inquest concluded that he had committed suicide by cyanide poisoning, although some historians have pointed out that the evidence is not entirely conclusive. The UK did not issue a formal apology until 2009, and Queen Elizabeth II posthumously pardoned him in 2013.
The legend of Apple
The idea that Apple's logo—a bitten apple—is a tribute to Turing has circulated for decades. It's a much-repeated story, but both the logo's designer, Rob Janoff, and Apple have explicitly denied it: they maintain that the "bite" was only added so that, at a small size, the silhouette wouldn't be mistaken for a cherry. The coincidence remains unproven, but the story has never stopped being told.