The British mathematician who founded theoretical computer science, broke the Enigma cipher during the Second World War, and asked 'Can machines think?' — defining the questions that artificial intelligence has pursued ever since — before being prosecuted for homosexuality and dying at 41.
Turing defined what a computer is before computers existed. He broke the Enigma code and may have shortened the Second World War by years. He asked whether machines can think. Then the British government prosecuted him for being gay, subjected him to chemical castration, and he died at 41. The full meaning of his life and work is still being worked out.