Mastermind born in turbulent reign (8)
I believe the answer is:
engineer
'mastermind' is the definition.
('engineer' can be a synonym of 'mastermind')
'born in turbulent reign' is the wordplay.
'born' becomes 'nee' (I've seen this before).
'in' is an insertion indicator.
'turbulent' is an anagram indicator.
'reign' anagrammed gives 'engir'.
'nee' placed inside 'engir' is 'ENGINEER'.
(Other definitions for engineer that I've seen before include "Bring about, being skilled in machinery" , "One can be chemical, civil or mechanical" , "Skilled professional - electrical, civil or mechanical" , "Applied technologist" , "One uses science to solve practical problems" .)