Alan Turing

Alan Turing was an English mathematician. During World War II, he was a code-breaker. He committed suicide in the mid-1950s.

Biography
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 Eighth Doctor crack an alien code in 1944. (EDA: The Turing Test)

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

The Eleventh Doctor and Amy Pond met a robot duplicate of Alan Turing in the Museum of Lost Opportunities. Although appearing to possess many of Turing's memories and attitudes, the robot did not remember Turing's previous encounter with the Doctor. (DWM: The Child of Time)