(Japanese: “heavenly emperor”), the title of Japan's chief of state, bestowed posthumously together with the reign name chosen by the emperor (e.g., Meiji Tennō, the emperor Meiji). The term was first used at the beginning of the Nara period (710–784) as a translation of the Chinese t'ien-huang, or “heavenly emperor,” and replaced the older title of mikado, or “imperial gate.”

According to Japanese tradition, the imperial line was founded in 660 BC by the legendary emperor Jimmu, a direct descendant of the sun goddess Amaterasu. Around the 3rd century AD, the imperial clan defeated rival chieftains and first asserted suzerainty over central and western Japan. The imperial institution survived for 2,000 years despite the removal of individual emperors and murders resulting from court intrigues. From the 12th to 19th century, however, aristocratic and military clans held virtually all the emperor's power (see shogunate). In 1868 the leaders of the Meiji Restoration claimed the reestablishment of direct imperial rule and built a centralized nation-state with the emperor as the symbol of national unity; loyalty to the emperor was made a sacred duty and a patriotic obligation, though he was actually given few governmental responsibilities.

The high priest of the Shintō cult and of divine ancestry, the Japanese emperor had been invested with an aura of sacred inviolability. The defeat of Japan in World War II dealt a blow to the emperor cult and the ancient myths of divine origin; the postwar constitution referred to the emperor as a symbol of the state, without effective political power.