The three pure ones
In Taoist mythology, there are three San-qing, one for each heaven. They are:
Yuan-shi tian-zong* in Yu-qing (Heaven of Jade Purity)
Creator and Master of Heaven and Earth.
Ling-bao tian-zong in Shang-qing (Heaven of Great Purity)
Guardian of the Tao, Master of time.
Tao-de tian-zong in Tai-qing (Heaven of the Highest Purity)
Revealer of the Tao.
The San-qing have existed since the beginning of time.
* Some stories claim that Yu-huang rules, or helps rule, Yu-qing.