Infamous tsar (4)
I believe the answer is:
ivan
'infamous tsar' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ivan that I've seen before include "- - the Terrible (Czar)" , "One Day in the Life of - Denisovich (Solzhenitsyn)" , "Russian tsar called 'the Terrible'" , "Russian ruler - a Terrible one" , "Chap" .)