Forebear (12)
'forebear' is the definition.
(a forebear is an ancestor or predecessor)
This is all the clue.
(Other definitions for ancestor that I've seen before include "Old member of the family -no traces (anag)" , "Adam was our first one" , "Predecessor" , "one is up a tree" , "One of one's forebears" .)
'forebear' is the definition.
(thesaurus)
This is all the clue.
(Other definitions for antecedent that I've seen before include "Something logically preceding another" , "prior" , "Previous" , "Going before (in time/order)" , "Preceding in time or order" .)
(Another definition for primogenitor that I've seen is " Patriarch".)