Bolshevik left over nine letters (5)
I believe the answer is:
lenin
'bolshevik' is the definition.
(I know that Lenin is a bolshevik)
'left over nine letters' is the wordplay.
'left' becomes 'l' (common abbreviation).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'letters' is an anagram indicator.
'nine' with letters rearranged gives 'enin'.
'l'+'enin'='LENIN'
(Other definitions for lenin that I've seen before include "Revolutionary leader" , "Communist leader" , "Early Soviet leader" , "First Soviet leader" , "Head of the Communist state after the fall of the Tsar" .)