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.
Constitution of Japan
Under the constitution, the Emperor is "the symbol of the State and of the unity of the people". The Emperor carries out most functions of a head of state, formally appointing the Prime Minister and Chief Justice of the Supreme Court, convoking the National Diet and dissolving the House of Representatives, under the advice of the Cabinet, and also promulgating statutes and treaties and exercising other enumerated functions.