Old Kai (老界王神, Rō Kaiōshin) is a deity from the fifteenth generation of Kai, now acting as the Grand Supreme Kai of Universe 7.
In the past, the Old Kai visited Zeno three times.
One day, an Old Witch snuck up on the Former Supreme Kai while he was reading a comic book and took one of the Potara Earrings that he was wearing, leaving the Supreme Kai with a horrified expression as he knows about the abilities of the Potara Earrings. She put the earring on her ear which caused the two to fuse. This caused him to become an old wrinkly being with a personality befitting of the new form, as well as new magical powers. Once every 1,000 years, the Supreme Kais and the Gods of Destruction go to each other's realms and hold a coordination meeting. During one of these meetings, held roughly 75 Million Before Age, they got into an argument over some trifling thing and a certain short-tempered, Beerus, sealed Old Kai away inside the Z Sword as it would not have been proper for him to destroy the Sacred World of the Kais itself. According to Old Kai, the person who sealed him inside the sword was very powerful but not as powerful and bad as Majin Buu.
Majin Buu Saga
Main articles: Fusion Saga and Kid Buu SagaShin and Kibito were looking for warriors they believed would be strong enough to defeat Majin Buu. They eventually ended up with Gohan and had him remove the Z-Sword from its stone encasement. Goku eventually showed up, and started to help Gohan train. To test the blade, Shin generated a cube of the strongest metal in the universe, Katchin, and gave it to Goku to throw. When Gohan hit the metal, the Z Sword broke in half, releasing Old Kai. After Old Kai expressed disappointment in Shin and Kibito for not breaking the sword's seal yet Gohan, a mortal, was able to break it, Goku tried to test Old Kai's power level by throwing a basic Ki Blast at him, with little enough power to deflect, and it instead knocked Old Kai down, resulting in Old Kai scolding Goku.
Old Kai told them that he could bring out Gohan's latent abilities by doing an "essential ritual". After waiting for well over an entire day, Old Kai had finally unleashed Gohan's hidden potential. After Gohan lost to Super Buu, Old Kai revealed the method of Potara Fusion to Goku and gave him the Potara Earrings to fuse with Gohan, (though Goku would end up fusing with Vegeta, creating Vegito).
He then gives up his life to Goku so he can return to Earth to fuse with Gohan and defeat Buu. When they decided to use the Namekian Dragon Balls to restore Earth and revive everyone, Old Kai refused to use them, as he claims that they would disrupt the balance of nature. However, he went along with it when Goku reminded him of his deal regarding his groping/gaining nude pictures of/going on a date with a human woman, with Goku inadvertently admitting in front of Vegeta that the woman in question was Bulma. When Super Buu reverted to Kid Buu, Old Kai went to Namek with Dende and Kibito Kai, where he and the others used the Namekian Dragon Balls to help Goku and Vegeta defeat Kid Buu. Old Kai was brought back to life by the wish made to Porunga to revive everyone who died after the 25th World Martial Arts Tournament, and so his halo disappeared after the wish was made.
Dragon Ball: Yo! Son Goku and His Friends Return!!
Two years after Buu's defeat, Old Kai, along with Kibito Kai, is on Earth at Mr. Satan's banquet at his newly made hotel in celebration of defeating Buu. The celebration is interrupted by a brother duo, Abo and Cado, whom are after Vegeta's brother Tarble. The brothers are challenged by Goten and Trunks but they fail in defeating them. The brothers, merged as Aka, unleash a technique that destroyed the hotel. Aka is then defeated by Goku with a Kamehameha. After this encounter, they continue their feast.
Dragon Ball Z: Battle of Gods
Four years after the battle with Majin Buu, Old Kai is with Kibito Kai when they and King Kai are telepathically discussing the awakening of the God of Destruction Beerus. They appear again after Goku's battle against Beerus and comment on Goku befriending the God of Destruction.