forefather vs ancestor

forefather and ancestor both are nouns.

Word	Noun	Adjective	Verb	Adverb
forefather	Yes	No	No	No
ancestor	Yes	No	No	No

As nouns, ancestor is a hypernym of forefather; that is, ancestor is a word with a broader meaning than forefather:

forefather: the founder of a family
ancestor: someone from whom you are descended (but usually more remote than a grandparent)

Other hypernyms of forefather include antecedent, ascendant, ascendent, root.

forefather (noun)	ancestor (noun)
the founder of a family	someone from whom you are descended (but usually more remote than a grandparent)
person from an earlier time who contributed to the tradition shared by some group