Forefather, once tsar, taken out (8)
I believe the answer is:
ancestor
'forefather' is the definition.
(I've seen this before)
'once tsar taken out' is the wordplay.
'taken out' indicates anagramming the letters.
'once'+'tsar'='oncetsar'
'oncetsar' is an anagram of 'ANCESTOR'.
(Other definitions for ancestor that I've seen before include "Old member of the family -no traces (anag)" , "An escort (anag.)" , "descent comes from one" , "Person from whom one is descended" , "Enactors (anag)" .)