A symbol, a prop. A man lies dead, and beside him is a half eaten apple. It is 1954, a cruel time for a man like this one. When they open him up, they will find him dead of cyanide poisoning. What, then, does the apple mean? Was it meant as a reference to his favourite fairy tale, Snow White? Was it meant as an homage to the man’s hero, Newton? Or was the inventor of the computer merely enjoying a snack before he took his own life?

There is, of course, no “inventor” of the computer. That kind of “Great Man” thinking is for Stalinists, and for dramatic internet story leads. (See above.) But if the history of the computer does have something of a father figure — if there is one man whose specific streak of genius runs through the story like a meme — than it must be that of Alan Turing.

Born June 7, 1912, and hounded to death by the intolerance of men and women so inferior to him in intellect that they were barely of the same species, Turing is one of the rare 20^th century figures even more present a hundred years after his birth.

Turing was given 42 years to change the course of history. I use the term “given”, because by the laws of the day, his sexual orientation was a crime, and he was unable to live as someone he wasn’t. “IEKYF ROMSI ADXUO KVKZC GUBJ”, reads a plaque under a statue of the man in a Manchester park. That is how “The Founder of Computer Science” reads in Enigma code — a code he helped break, thus hastening the end of World War II. Turing’s intellectual fingerprints are all over the major innovations of the previous century; he weaves in and out of history like the ciphers he once helped break.

No one ever mistook Turing for anything other than a genius. Sure, there were masters at Sherbonne School who couldn’t abide his disinterest in the classics, mostly because mathematics ran a distant second to Ancient Greek. Still, he was so bright that when he was 16, he mashed through Albert Einstein’s work, unearthing nuggets of Newtonian brilliance that were never obvious in the text. Finding this sort of proto-Easter egg was all in a days work for Turing, who didn’t bother learning calculus, mostly because he was born with its principles in his head.

Then came King’s College, Cambridge. Time to shine. And shine Turing did. That was largely because of the earth-shattering “On Computable Numbers, with an Application to the Entscheidungsproblem” — a paper, delivered in 1936, that introduced something called the Turing machine. This was not a mechanical object in the traditional sense of the term— no whirring metal parts or electrical wiring — but the idea for a machine. It described a set of hypothetical formulae that their devisor insisted would be able to solve any mathematical problem should it be reformulated as an algorithm. A machine that could compute infinitely.

Off he went to Princeton, furthering his reputation by studying with the great Alonzo Church, then back to Cambridge. When World War II broke out, Turing was suddenly thrust into the role of hero. He was not about to mow down Nazis with a Gatling gun, although he was an impressive physical specimen — a long-distance runner, and a natural athlete. But it was his brain that the war effort wanted. He was cosseted in the legendary Bletchley Park. And he went to war against German code.

Ah, the old days of thrust and parry! A code was enciphered; a code was deciphered. A machine was built, and another one built to pick through the parts on the other side of the channel. Turing’s contributions to the war effort were outrageous. In 1938, the Poles had figured out how to crack the German’s infamous Enigma machine; within weeks of arriving at Bletchley, Turing had devised a better way. He built, along with Gordon Welchman, a device called the British (later, the Turing) Bombe, which could break the code of almost any Enigma machine provided there was a plain-text crib.

The war transformed Turing into a high-level liason between Britain and the United States, and by 1943 he was out of Bletchley. The post-war years, however, put him in a unique kind of danger. He was a shy man, clearly homosexual, and quickly coming to terms with that fact. In the world of cloak and dagger, gay men with secrets were thought to be easy marks for the KGB.

Hi fate awaited him on the other side of his ideas for Artificial Intelligence. He wrote a simple chess-playing algorithm. He described the infant human cortex as “an unorganised machine”, and believed that a computer could be trained to be smarter. Here is Turing’s biographer, Alan Hodges:

“The vision of mechanical intelligence must have stimulated great excitement; I would now go further and suggest that it was at this period that he abandoned the idea that moments of intuition corresponded to uncomputable operations. Instead, he decided, the scope of the computable encompassed far more than could be captured by explicit instruction notes, and quite enough to include all that human brains did, however creative or original. Machines of sufficient complexity would have the capacity for evolving into behaviour that had never been explicitly programmed. And it was at this period that he also lost interest in logic as a tool for probing reality — although it must be said that he retained a keen interest in theoretical computability within mathematics, being one of the first into the field when it was yoked to algebra in the late 1940s.”

Turing had indeed lost his interest in mathematical logic, along with his understanding of human logic. He had met a man at the movies, and the man turned out to be something of a cur. After robbing Turing’s flat, the police were involved, and ended up charging Turing with gross indecency under the Criminal Law Amendment Act of, wait for it, 1885.

The quintessential 20^th century man was felled by a Victorian law. He opted for chemical castration to control his now-illegal libido. The shots of estrogen were, according to testimony from the day, unpleasant and unhelpful.

And so, the fatal apple. You may note that the same partially eaten fruit adorns the richest company in the world today. The Apple logo is not, according to Steve Jobs, a nod to Turing. But everything inside their product is. Alan Turing didn’t properly die, because he was coded into the information age. In the end, his immortality is the greatest rebuke to his castrators. DM

Read more:

• The Alan Turing Scrapbook
• Enigma film review on Cryptographic

Photo: An anatomical model of a human head is seen at an exhibition at the Wellcome Collection in London March 27, 2012. (REUTERS/Chris Helgren)