Statesman Berliner once beheaded (7)
I believe the answer is:
russian
'statesman' is the definition.
(person from Russia, a state)
'berliner once beheaded' is the wordplay.
'berliner once' becomes 'prussian' (Berlin was once part of Prussia).
'beheaded' means to remove the first letter (the head of the word is removed).
'prussian' with its initial letter taken off is 'RUSSIAN'.
(Other definitions for russian that I've seen before include "Muscovite possibly" , "Muscovite, maybe" , "Slav" , "Putin's language" , "Countryman" .)