Code-breaker Turing (4)
I believe the answer is:
alan
'code-breaker turing' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for alan that I've seen before include "Lana (anag.), man's name" , "-- Bennett, playwright" , "Boy's name" , "English historian/poet" , "A.A. Milne's first name" .)