Alan Turing ☆

Turing defined computation itself (1936), broke Enigma at Bletchley, and in 1950 posed machine intelligence as an empirical question with his imitation game. Every benchmark on this site descends from that move: replacing 'can it think?' with 'can it do the task?'. Persecuted by the British state for his homosexuality, he died in 1954; the field's highest award bears his name.