During the Second World War, Alan Turing worked at the Government Code and Cipher School at Bletchley Park – the forerunner of GCHQ – where he devised the techniques which cracked the German Enigma code.
Very smart man to devise the techniques to de-cipher the Enigma code. From the enigma and later lorenz machines. Very much like Joseph Rochefort who help break the Japanese "book cipher" codes of WW2.
These two men do not get the credit they deserve for their actions in shortening the war by letting us read almost all German and Japanese plans.