Supreme god of the ancient Greeks (4)
I believe the answer is:
zeus
'supreme god of the ancient greeks' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for zeus that I've seen before include "Great being in Greece" , "Greek god - husband and brother of Hera" , "Top Greek god" , "Divine son of Cronos and Rhea" , "Suez (anag)" .)