From Early Historical Times to the Mid-12th Century

The title tenno (literally "heavenly sovereign") was first assumed by Japanese rulers in the 6th or 7th century and has been used by all subsequent Japanese sovereigns.

Japan’s imperial institution, the oldest hereditary monarchy in the world, was already in existence when Japan emerged into recorded history and has since been perpetuated in a predominantly male line of descent. Although the emperor has almost always been regarded as the titular head of the national government, the most striking feature of the office through most of Japanese history has been the tendency to emphasize instead the emperor’s role as chief priest in the indigenous Japanese religion, Shinto, and to delegate most of the effective powers of government to others.

The emperor figures centrally in a mythology preserved in the historical chronicles Kojiki (712, Record of Ancient Matters) and Nihon shoki (720, Chronicle of Japan). According to these, the sun goddess Amaterasu Omikami, chief divinity of the Shinto pantheon, bequeathed to her grandson Ninigi no Mikoto a mirror, jewels, and a sword, which he in turn passed on to his descendants, the emperors of Japan, the first of whom was the emperor Jimmu.

The emperor was thought to possess magical powers to propitiate or intercede with divinities. But because of the awe surrounding his person, it was also considered inappropriate for the emperor to concern himself with the secular business of government. That business, including both the making and execution of policies, belonged to ministers serving the emperor, and there was a tendency from very early historical times for those ministers to form political dynasties of their own.

The only extended period of Japanese history in which the emperor combined the roles of both high priest and functioning head of government was from the reign of Tenji (r 661-672), in the latter half of the 7th century, through the reign of Kammu (r 781-806) at the end of the 8th century and the beginning of the 9th. It was Tenji who, in the Taika Reform of 645, made the first major attempt to bring the powerful provincial clans (uji) under the control of a strong central regime.