Emperor Suinin
In the 13th century, Jien recorded in the "Gukanshō" that during the reign of Emperor Suinin, the first High Priestess ("saiō") was appointed for Ise Shrine. Hayashi Gahō's 17th century "Nihon Ōdai Ichiran" is somewhat more expansive, explaining that since Suinin's time, a daughter of the emperor was almost always appointed as high priestess, but across the centuries, there have been times when the emperor himself had no daughter; and in such circumstances, the daughter of a close relative of the emperor would have been appointed to fill the untimely vacancy.