the father of one's father or mother.

a forefather.

the founder or originator of a family, species, type, etc.; the first of one's or its kind, or the one being longest in existence

the grandfather of all steam locomotives.

to exempt (something or someone) from new legislation, restrictions, or requirements

The law grandfathered all banks already operating at the time of passage. He was grandfathered into the pension plan.

noun

paternal forebear , elder , forefather , ancestor , patriarch , grandpa , granddaddy , grandpappy , granddad , pap , gramps