Supreme Kai is the ruler of the entire Universe. He is a very wise and rational person. Thousands of years ago he was originally the Eastern Supreme Kai who served under the Grand Supreme Kai; before Majin Buu defeated him and the Northern, Southern and Western Supreme Kais.
When Majin Buu became a threat once again he traveled to Earth with his bodyguard Kibito and joined forces with the Earth's greatest heroes.
Although a very powerful fighter he was constantly surprised at the power of Goku and his friends; which surpassed his own power. Later he used the Potara Earrings to permanently fuse with Kibito to become Kibito Kai.
In the English dub version of the Dragon Ball Z anime series by Funimation Supreme Kai was voiced by Kent Williams.
In an alternate English dub by the Ocean Group Supreme Kai was voiced by Michael Dobson.