In 1936, a 24-year-old Cambridge mathematician published a paper that would change the world. The paper, "On Computable Numbers," described a hypothetical machine — now called a Turing machine — that could, in theory, compute anything that is computable. This was the mathematical blueprint for every computer ever built. The mathematician's name was Alan Turing.
Turing's concept was abstract but profound. He imagined a machine that reads symbols on a tape, follows rules, and writes new symbols. Simple as that sounds, he proved that such a machine — given enough tape and time — could simulate any other computational process. This is the foundation of what we call universal computation: the idea that one machine can emulate any other machine.
When World War II began, Britain needed Turing's mind more than ever. He joined Bletchley Park, the top-secret codebreaking center in Buckinghamshire. The Germans were using an encryption machine called Enigma to communicate, and the Allies could not read their messages. Turing and his team built an electromechanical device called the Bombe that could, in hours, find the daily Enigma settings — breaking the code that the Germans thought was unbreakable.
Historians estimate that Turing's work at Bletchley Park shortened World War II by two to four years and saved millions of lives. Winston Churchill reportedly said that Turing made the single biggest contribution to Allied victory of any individual. After the war, Turing moved to Manchester, where he helped design one of the world's first stored-program computers.
In 1950, Turing published another landmark paper: "Computing Machinery and Intelligence." It opened with a deceptively simple question: "Can machines think?" He proposed what he called the Imitation Game — later known as the Turing Test — as a way to evaluate machine intelligence. The test remains a touchstone of artificial intelligence philosophy to this day.
In 1952, Turing was arrested. His crime: gross indecency — the British legal term for homosexual acts, which were criminal at the time. He was given a choice between prison and chemical castration through hormone injections. He chose the injections. His security clearance was revoked. He was banned from his own work.
On June 7, 1954, Alan Turing was found dead. A half-eaten apple was found beside him, and the coroner ruled it suicide by cyanide poisoning. He was 41 years old. Some believe the apple was a reference to Snow White — the poisoned apple — and that it was a final act of dark poetry from a man who had spent his life thinking in symbols.
In 2009, British Prime Minister Gordon Brown issued a formal apology for Turing's treatment. In 2013, Queen Elizabeth II granted him a posthumous royal pardon. Today, Turing appears on the British £50 note — the country's highest-denomination bill. The computer science world's most prestigious award, given annually by the ACM, is called the Turing Award. It is often described as "the Nobel Prize of computing."