Alan Turing

Alan Turing was an English mathematician. During World War II, he was a code-breaker with whom both Rachel Jensen and Toshiko Sato's grandparents worked. (PROSE: Who Killed Kennedy, TV: Greeks Bearing Gifts)

During the war, he designed a Rift Predictor for Torchwood Three in 1941 (PROSE: The Twilight Streets) and cracked the code at Bletchley Park in spring of that year. (AUDIO: Criss-Cross) Although strictly confidential, WREN Constance Clarke was present that morning and knew the work was instrumental to the war effort, changing the tide of the war. (AUDIO: Criss-Cross)

The Second Doctor remembered meeting Alan and observing how glowing parts in his huge computers attracted insects, which resulted in the term "bug" being born. (AUDIO: The Uncertainty Principle)

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

He committed suicide in the mid-1950s, after having been hounded out of academia by Professor Jeffrey Broderick. (AUDIO: Artificial Intelligence)

Duplicates and alternatives
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. (COMIC: The Child of Time)

In an alternative timeline, Turing was the inventor of the Turing Shroud, which served as a schematic of an early computer, only to be arrested on charges of sexual deviancy by the Star Chamber in 1936 before he could do any serious work. He was kept locked up in the Tower of London until 2003 when he was executed by this timeline's version of Sabbath, who had been manipulated into believing that Turing's death would separate his world from the rest of the universe as alternate timelines began to collapse, but Turing's death actually accelerated the damage and destroyed this reality due to his status as the main focal point of this word's divergence from other histories. (PROSE: The Domino Effect)

Behind the scenes

 * He was played by Benedict Cumberbatch in the 2014 film The Imitation Game and by Derek Jacobi in Breaking the Code.