Yoshihito, (1879–1926), the 123rd emperor of Japan. During his reign Japan joined the Allies in World War I, won important German islands in the Pacific, and rose to the position of a leading world power. Yoshihito succeeded to the throne in 1912, after the death of his father, Emperor Mutsuhito. Because of mental illness, Yoshihito was in seclusion from 1920 until his death. Hirohito, his son and successor, acted as regent.