Notorious czar (4)
I believe the answer is:
ivan
'notorious czar' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ivan that I've seen before include "- - the Terrible (Czar)" , "'Terrible' emperor of Russia" , "Fellow" , "Russian ruler - a Terrible one" , "Vain (anag) - Tsar of Russia" .)