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 of Japan
Article 2 of the Constitution of Japan, promulgated in 1947 by influence of the U.S. occupation administration, provides that "The Imperial Throne shall be dynastic and succeeded to in accordance with the Imperial Household Law passed by the Diet." The Imperial Household Law of 1947, enacted by the ninety-second and last session of the Imperial Diet, retained the exclusion on female dynasts found in the 1889 law. The government of Prime Minister Yoshida Shigeru hastily cobbled together the legislation to bring the Imperial Household in compliance with the American-written Constitution of Japan that went into effect in May 1947. In an effort to control the size of the imperial family, the law stipulates that only legitimate male descendants in the male line can be dynasts; that imperial princesses lose their status as Imperial Family members if they marry outside the Imperial Family; and that the Emperor and other members of the Imperial Family may not adopt children. It also prevented branches, other than the branch descending from Taishō, from being imperial princes any longer.