Supreme Kai is the supreme ruler of the Eastern Quadrant of the Universe. He is short, purple skinned with white hair, dressed in a posh Kaio outfit and always accompanied by his ever-loyal bodyguard and friend, Kibito.
Supreme Kai has purple skin, black eyes and a white mohawk. He wears the standard Kai outfit.
When first introduced and during his brief match-up with Piccolo, Supreme Kai remained calm and was rather mysterious. His personality started to change after witnessing Saiyan power and the return of Majin Buu. He became more fearful, cautious and dependent on Goku and the others.
Major Story Arcs
Dragon Ball Z
East Kaioshin survived Majin Buu's assault on the Kaioshin Kai to become the only surviving Kaioshin, when rescued by his bodyguard. East Kaioshin mentions that he was the weakest of the four kaioshins. Majin Buu proved even too powerful for his creator, the great wizard Bibidi, which forced him to seal up his destructive creation. Without Buu, the Supreme Kai was able to kill the wizard.
Afterward he is typically called only Kaioshin, since there are no others to confuse him with. He placed Buu on Earth, not knowing that Bibidi had an evil son, Babidi, with the same evil goals.
Once he learned of this, Supreme Kai and Kibito left for Earth and recruited Goku and the other Z-Fighters to aid them in Babidi's defeat. They were unsuccessful and Majin Buu was revived.
Supreme Kai faced Buu once again and fared no better. He and Kibito retreated to their sacred world, bringing Gohan with them in the hopes he could pull the powerful Z-Sword from it's stone. Gohan was successful, but it turned out the sword wasn't what was powerful. The Elder Kai had been trapped inside. Once released, he amplified Gohan's power emmensly. He also told Supreme Kai of the Potara earrings they wore and their ability to fuse two beings together. Supreme Kai fused with Kibito, only to find out after that the fusion was permanent.
After this, Supreme Kai was known as Kibito Kai.
Dragon Ball Super
When the Kais learned the Champa the God of Destruction of the Sixth Universe was hunting the Dragon Balls, Kibito Kai gathered the Namekian set to safeguard them. When they learned that he was looking for a different set, Kibito Kai used the balls to wish to separate the Potara fusion. Supreme Kai and Kibito became individuals once again.
Due to having little feats and very few fighting scenes, Supreme Kai's exact power is unknown but he stated that he is much more powerful than Frieza and that he can defea Frieza in only one blow. Piccolo also became surprised at Supreme Kai's power and stated that his power is dimensions away from his own which implies that Supreme Kai may be stronger than Piccolo but this may prove otherwise as Supreme Kai became fearful and shocked after seeing Yakon who is stronger than Frieza. Supreme Kai was able to restrain SSJ2 Gohan.
Supreme Kai was able to fight against Fat Buu and deal some blows but that was all he could do against the monster.
Supreme Kai has some powerful magic abilities. He can restrain Gohan and save Gohan from getting killed by Fat Buu.