The clan comprising the descendants of Fujiwara, Kamatari (614-669) who rose to power in the mid-seventh century assisting the imperial prince to make reforms which eventuated in the ritsuryo system. The Fujiwara family remained intertwined through marriage and government positions with the imperial line. Fujiwara, Yoshifusa (804-872) became 'regent' (sessho) when a child emperor was enthroned in the mid-ninth century and his adopted son became both regent and chief counsellor (kanpaku) of the imperial family. By virtue of these hereditary appointments which continued regardless of the age of subsequent emperors the Fujiwara became effectively the rulers of medieval Japan until the mid-eleventh century.
A Popular Dictionary of Shinto. Brian Bocking.