In 1935 theoretical mathematician Alan Turing proposed a machine that would use a series of on and off switches that could represent or compute anything.
Turing joined the war effort to build mechanical computers that decrypted Enigma messages. Eventually, he helped with electronic computers. His theories underpin all modern computers.
Subsequently, Turing envisaged reasonably sentient artificial intelligence, an idea that was ridiculous in his time. He ultimately developed the “Turing Test,” where a person could not tell whether they were communicating with a person or a computer. As of 2019, no computer program has yet to pass the Turing test.
Because of a conviction for homosexuality Turing was banned from computers on national security grounds. Subsequently, he committed suicide in 1954.