Empress Kōgyoku (皇極天皇) or Saimei (斉明天皇) (594-661) was the 35th imperial ruler of Japan. From 642 she ruled as Kogyoku, but abdicted after the assasination of Soga no Iruka and gave the throne to her brother Kotoku in 645. After Kotoku died in 655, she reascended the throne as Saimei, and ruled under that name until her death. She was a third generation granddaughter of Emperor Bidatsu. Her birth name was Princess Takara.

She was the wife and empress of the Emperor Jomei. They had three children: Prince Nakanooe (Tenji), Prince Oama (Temmu), and Princess Hashihito. After the death of her husband, she ascended the throne.

During her first reign the clan of Soga seized power. Her son Nakanooe planned a coup d'etat and slayed Soga no Iruka at the court in front of her throne. The clanhead, Soga no Umako fired his mantion when he got this report and the clan of Soga declined. She was very shocked with this incidence and descended the throne.

After Emperor Kotoku died, though Nakanooe was the crown prince, he had his mother reascend the throne, and remained as the crown prince of her mother. But he seized the power and led the politics of Japan. At the end years of her reign, Baekje in Korea was destroyed in 660, in the 5th year of her second reign. Japan assisted Baekje loyals to the attempt of retrieving former Baekje territory. In the early of 661, With army and navy Saimei started from the capital in Yamato province in Honshu, crossed the Seto Inland Sea from east to west. She stayed Ishiyu Temporary Palace in Iyo province, today Dogo spa. On May arrived Asakura Palace in the north part of Chikushi province in Kyushu, today a part of Fukuoka prefecture. The allied army of Japan and Baekje was prepared the war against Silla but on July 24 (Japanese calender), 661 she died in the Asakura Palace before the army departed to Korea. On October her body departed from Kyushu by sea and arrived Port Naniwa-zu (today Osaka city). Her funeral celemony was held on the early November.

After her death, her son Nakanooe ascended to the throne in 663, after the battle against Silla and Sui Dynasty.