Cryptanalyst Turing (4)
I believe the answer is:
alan
'cryptanalyst turing' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for alan that I've seen before include "-- Turing, English computer scientist" , "One of Robin Hood's men was - a Dale" , "Boy's name" , "- Bates, - Bennett" , "English historian/poet" .)