Taira no Kiyomori
Taira no Kiyomori was the head of the Taira clan in the 1150s until his death in 1180, and an extremely influential and powerful figure at Court for much of that period. Following in the footsteps of the Fujiwara clan, he came to dominate court politics, both through political marriages and other means, becoming the de facto ruler of the State for over two decades, suppressing the power of the Retired Emperors, and having reigning emperors as, essentially, puppet rulers. His rise to power marks the beginning of the rise of samurai power, and the end of direct Imperial rule; his fall, or, rather, that of his clan, is the chief theme of the great epic The Tale of the Heike (Heike monogatari).
Kiyomori was the son of Taira no Tadamori and grandson of Taira no Masamori, who served as "close retainers" (kinshin) within the "cloistered court" (in-no-chô) of Retired Emperors Shirakawa and Toba. As a result, even from the young age of 12, Kiyomori already began to receive special preference in court rank and official positions.
Along Minamoto no Yoshitomo, he led Emperor Shirakawa's forces to victory in the Hôgen Disturbance of 1156, and then led the Taira clan to victory again in 1159, crushing Yoshitomo, who had become his rival for power, in the Heiji Disturbance. Through both of these victories, Kiyomori gained and then secured considerable power, becoming one of the "senior nobles" (kugyô) by 1160, and daijô daijin ("Chancellor of the Realm") in 1167, flying up through the ranks without even passing through the positions of Minister of the Left and of the Right (Sadaijin and Udaijin).
He further secured his elite position by marrying the sister of Kenshunmon-in, a favored consort of Emperor Go-Shirakawa; this also made him uncle (by marriage) to Emperor Takakura. One of Kiyomori's daughters, who would later be known as Kenreimon-in, became a consort to Takakura, while other daughters of Kiyomori were married to prominent members of the Fujiwara clan.
Kiyomori fell ill in 1168 and formally retired from official service; he retained considerable power and influence, however.