First head of the USSR (5)
I believe the answer is:
lenin
'first head of the ussr' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for lenin that I've seen before include "Revolutionary man" , "Revolutionary leader" , "Russian revolutionary" , "Soviet Union's first premier" , "Vladimir Ilyich Ulyanov, d. 1924" .)