Name and title
Jimmu is recorded as Japan's first ruler in two early chronicles, Nihon Shoki (721) and Kojiki (712). Nihon Shoki gives the dates of his reign as 660–585 BC. In the reign of Emperor Kanmu (737–806 AD), the eighth-century scholar Ōmi no Mifune designated rulers before Ōjin as tennō (天皇, "heavenly sovereign"), a Japanese pendant to the Chinese imperial title Tiān-dì (天帝), and gave several of them including Jimmu their canonical names. Prior to this time, these rulers had been known as sumera no mikoto/ōkimi. This practice had begun under Empress Suiko, and took root after the Taika Reforms with the ascendancy of the Nakatomi clan.
According to the legendary account in the Kojiki, Emperor Jimmu was born on February 13, 711 BC (the first day of the first month of the Chinese calendar), and died, again according to legend, on April 9, 585 BC (the eleventh day of the third month).
Both the Kojiki and the Nihon Shoki give Jimmu's name as Kamu-yamato Iware-biko no mikoto (神倭伊波礼琵古命/神日本磐余彦尊). Iware indicates a toponym whose precise purport is unclear.
The Imperial House of Japan traditionally based its claim to the throne on its putative descent from the sun-goddess Amaterasu via Jimmu's great-grandfather Ninigi.