Taishō (tĪˈshō) [key], 1879–1926, reign name of emperor of Japan (1912–26). His given name was Yoshihito. The son of Mutsuhito, the Meiji emperor, he succeeded to the throne in 1912, but because of illness he played little part in governing the nation. His reign was characterized by democratization, friendly relations with the West, and economic growth. In 1921 Taishō was declared mentally incompetent and his son Hirohito was made regent.