Four Heavenly Ministers (Si4 Yu4 Da4 Di5)
Origin of the Four Heavenly Ministers
The Four Heavenly Ministers, including the Heavenly Lord Zi Wei of the Northern Polar in the Middle Heaven, the Great Heavenly Lord of the Highest Palace of Polaris, Heavenly Lord of the Southern Polar of Longevity and the Imperial Goddess of Earth(Hou Tu), are four deities in charge of all things in Heaven and Earth under the Three Pure Ones(San Qing) and they assist the Great Jade Emperor in all administrative work.
The Great Jade Emperor is the master of the ten thousand spirits.
Heavenly Lord Zi Wi, as the Stellar Sovereign is the master of all the stars.
The Great Heavenly Lord of the Highest Palace of Polaris, which is composed of four stars left of the Imperial Polar Constellation, is located at the Pole Star as the pivot of heaven, in charge of the Three Powers in Heaven.
The Imperial Goddess of Earth is the center of Heaven and Earth; it had a a male form before the Tang dynasty and acquired a female form during Wu Zetian's reign.
Functions
The Great Jade Emperor, subordinate only to the Three PureOnes, is in charge of the Tao of heaven.
The Heavenly Lord Zi Wei assists the Jade Emperor in administering the longitudes and latitudes of Heaven and Earth, the sun, the moon and stars, as well as the climate of the four seasons. He is honored as the "master of all stars and assistant sovereign of the three realms"
The Great Heavenly Lord of the Highest Palace of Polaris, aka Heavenly Lord Tian Huang is in charge of the Three Powers of Heaven, Earth and Man, and of wars in the human world.
The Imperial Goddess of Earth is in charge of births, land, rivers, and mountains.
The Heavenly Lord of the Southern Polar of Longevity is in charge of all spirits and life and death of all beings
In large scale Taoist rituals and ceremonies, it is common to see the altar having the Four Heavenly Ministers(Si Yu), either beside or just under the Jade Emperor. These four divines ranked just below the Jade Emperor and they are similar to the deputy Prime Minister in modern days. Therefore they are highly respect in the Taoist religion.