Alan Turing

Alan Turing is an English mathematician and code-breaker during World War II

Rachel Jensen and the grandparents of Toshiko Sato worked with Turing. (MA: Who Killed Kennedy, TW: Greeks Bearing Gifts)

Turing designed a Rift Predictor for Torchwood Three in 1941 (TWN: The Twilight Streets)

Turing helped the Doctor crack an alien code in 1944. (PDA: The Turing Test)

In an alternate timeline Turing was the inventor of the Turing Shroud. (EDA: The Domino Effect)