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
Until recent centuries, Japan's territory did not include several remote regions of its modern-day territory. The name "Nippon" came into use only many centuries after the start of the current imperial line. Centralized government only began to appear shortly before and during the time of Prince Shōtoku (572–622). The Emperor was more like a revered embodiment of divine harmony than the head of an actual governing administration. In Japan, it has always been easy for ambitious lords to hold actual power, as such positions have not been inherently contradictory to the Emperor's position. The parliamentary government today continues a similar coexistence with the Emperor as have various shoguns, regents, warlords, guardians, etc.