Dai Kaiōshin (大界王神; lit. "Grand God King of the Worlds"), or Daikaioh in the FUNimation dub, is the highest of all Kaioshin and rules over the entire universe before the series takes place. His story is told in East Kaioshin's flashback, in the manga he is only seen for one panel but the anime expands on more of his backstory.
When Majin Buu comes to the planet, Dai Kaioshin manages to save the East Kaioshin from Buu's attack and unleashes a powerful attack of his own that blasts Buu into pieces. However, the Dai Kaioshin gets absorbed seconds later. After the Dai Kaioshin was absorbed, Buu takes a form that looks remarkably similar to Dai Kaioshin. This "fat" Buu would continue to show the Dai Kaioshin's spirit within him and later even becomes Mr. Satan's friend. The Dai Kaioshin's presence within Buu pacifies him.