Emperor Jimmu was the legendary first emperor of Japan according to the Nihon Shoki and Kojiki. His ascension is traditionally dated as 660 BC. In Japanese mythology, he was a descendant of the sun goddess Amaterasu, through her grandson Ninigi, as well as a descendant of the storm god Susanoo. He launched a military expedition from Hyūga near the Seto Inland Sea, captured Yamato, and established this as his center of power. In modern Japan, Emperor Jimmu's legendary accession is marked as National Foundation Day on February 11. There is no evidence to suggest that Jimmu existed. However, there is a high probability that there was a powerful dynasty in the vicinity of Miyazaki Prefecture during the Kofun period.

The emperor of Japan or Tennō , literally "ruler from heaven" or "heavenly sovereign", is the hereditary monarch and head of state of Japan. The emperor is defined by the Constitution of Japan as the symbol of the Japanese state and the unity of the Japanese people, his position deriving from "the will of the people with whom resides sovereign power". The Imperial Household Law governs the line of imperial succession. Pursuant to his constitutional role as a national symbol, and in accordance with rulings by the Supreme Court of Japan, the emperor is personally immune from prosecution. By virtue of his position as the head of the Imperial House, the emperor is also recognized as the head of the Shinto religion, which holds him to be the direct descendant of the sun goddess Amaterasu. According to tradition, the office of emperor was created in the 7th century BC, but the first historically verifiable emperors appear around the 5th or 6th centuries AD.