On the June 23 centenary of his birth in London, several cities will host conferences and exhibitions to celebrate the work of a man hailed as a rare genius today but persecuted for being gay when he was alive.

"Of all the finest types of intelligence -- human, artificial and military -- Turing is perhaps the only person to have made a world-changing contribution to all three," the science journal Nature said in a recent editorial.

Remembered as an eccentric with "an impish sense of humour", Turing died aged 41 of cyanide poisoning after he was convicted in 1952 of "gross indecency" for being homosexual, then illegal in the UK, and sentenced to chemical castration.

Some believe he took his own life by eating a poisoned apple in 1954, but this has not been proven.

In his short life, Turing lay the theoretical foundation for the modern-day computer, set the standard for artificial intelligence, unravelled German codes in a war effort some say saved millions of lives, and came close to solving a biological riddle that still confounds scientists today.