primogenitor(n = noun.person) progenitor - an ancestor in the direct line;
is a kind of ancestor, antecedent, ascendant, ascendent, root
has particulars: genitor

   The first ancestor; a forefather. [1913 Webster]

primogenitor, n.
1 the earliest ancestor of a people etc.
2 an ancestor.

Etymology:
var. of progenitor, after PRIMOGENITURE