Former Russian ruler (4)
(Other definitions for tsar that I've seen before include "Rats to the Russian emperor" , "Supreme authority" , "Potentate" , "Powerful man" , "Despot" .)
'former russian ruler' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for czar that I've seen before include "Despot" , "Russian ruler (alt. but not rare spelling)" , "person of great power" , "Russian emperor" , "policy coordinator" .)
(Other definitions for lenin that I've seen before include "Head of the Communist state after the fall of the Tsar" , "Revolutionary leader" , "V. I. -, Soviet politician and revolutionary" , "Vladimir Ilyich -, Soviet premier" , "Communist leader" .)