The earliest appellation Emperor was a general designation of Three Kings and Five Emperors. Three Kings were referred to Emperor of Heaven, Emperor of Earth and Emperor of Human, the three ancient emperors in Chinese legends. Originally, Emperor was referred to Emperor of Heaven, the sovereign ruler of everything on earth. Later on, after wars occurred between many states, their rulers called themselves emperor, such as Western Emperor, Eastern Emperor, Mid Emperor, Northern Emperor, and so on, which made the Emperors in the heaven come down into the world and thus became a honorific title in the world. (There was another saying that Five Emperors were referred to the Yellow Emperor, Emperor Yan, Emperor Ciyou, etc. in the tribe age.)

After the first emperor of the Qin Dynasty (221-206BC) unified the whole country, he regarded himself having more virtues than 'Three Kings' and obtaining more achievements than 'Five Emperors', and combined King and Emperor, the two superlative titles in the world, and took it as his appellation. From then on, the Sons of Heaven were called Emperors.