Infamous czar (4)
I believe the answer is:
ivan
'infamous 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 "A Russian emperor, quite Terrible" , "Name of six Russian tzars" , "One Day in the Life of - Denisovich (Solzhenitsyn)" , "'Terrible' emperor of Russia" , "First Russian tsar, 1547-84" .)