Records of heads of state
Officially, the current Emperor of Japan, Akihito is the 125th in line from the first emperor Jimmu, who is variously believed to have reigned in the 1st or 7th century BC. The earliest documentary evidence is only for the 29th emperor, Kinmei (AD 509–571); however, this is sufficient such that even the most conservative of estimates still places the Japanese imperial family as among the oldest lines in the world today.
Emperor
Japanese monarchs were given their official title by the Chinese emperor. The new Japanese monarch after coming into power would send a representative to China and receive the anointment. They would receive their official title on several golden plates of several meters tall. Since the Japanese monarchs changed their title to 天皇 (Heavenly Emperor) in 607, the Chinese emperor refused to anoint the Japanese king, thus, ending relations with Japan for the next few hundred years. Although the Japanese emperors used Chinese imperial titles, rarely was the Chinese-style "Son of Heaven" used. In the Japanese language, the word "tennō" is restricted to Japan's own monarch; "kōtei" (皇帝) is used for foreign emperors. Historically, retired emperors often kept power over a child-emperor as de facto regent. For a long time, a "shōgun" (formally the imperial generalissimo, but made hereditary) or an imperial regent wielded actual political power. In fact, through much of Japanese history, the emperor has been little more than a figurehead.