Born into the Isonokami clan that is descended from the powerful ancient clan of Mononobe (alleged to be the fifth-generation descendant of the younger brother of MONONOBE no Moriya who opposed the introduction of Buddhism), Yakatsugu is famed for his military accomplishments defeating FUJIWARA no Nakamaro and rising to the rank of Dainagon (chief councilor of state) but at the same time was a leading figure in literature and arts and an avid Buddhist.
古代の有力豪族であった物部氏の末裔（仏教反対派として有名な物部守屋の弟の5代目の子孫だとされる）である石上氏に生まれた宅嗣は藤原仲麻呂討伐などで活躍をして大納言にまで昇る一方で当時を代表する知識人・文人であり、熱心な仏教信者でもあった。