The Kaiō (or Kai in the English language dub of the anime) are upper-level gods of the fictional Dragon Ball universe. There are five per galaxy, with one presiding over each quadrant and the last (the Dai Kaiō) overseeing them all. The Kaiō are responsible for the lower-level gods (Kami) of the individual planets.
Above the Kaiō are the Kaiōshin, who look after the entire universe. Like the regular Kaiō, there is one for each quadrant and a Dai Kaiōshin to preside over them.
Kaio (Kai)
North Kaiō - The Kaiō of the quandrant of the galaxy where Earth resides. In the English dub, he is simply King Kai. In the English manga, he is also known as Lord of the Worlds.
East Kaiō
West Kaiō
South Kaiō
Dai Kaiō
Kaiōshin (Supreme Kai)
East Kaiōshin - The only surviving Kaiōshin of Buu's assault. Mostly just goes by Kaiōshin or Supreme Kai since he's the only one.
South Kaiōshin - Strongest of the Kaiōshin, he was absorbed by Buu.
North Kaiōshin - Killed by Buu.
West Kaiōshin - Killed by Buu.
Dai Kaiōshin - Absorbed by Buu, he made Buu become weaker and ammoral (as opposed to raw evil) due to his good nature.
Rou Dai Kaiōshin - A former Dai Kaiōshin from 15 generations back. He powers up Son Gohan.
Kibito - East Kaiōshin's loyal companion. Not actually a Kaiōshin himself.
Kibitoshin (Kibitokai) - Permanent fusion between Kibito and East Kaiōshin.
Kaiō is also a Japanese surname. It can refer to several people or fictional characters, including:
East Kai- is the only female among the ruling Kai's and controls the East quadrant of the universe, which is known for it's speedy fighters.
GrandKai is reputed as the greatest fighter in the universe, but hes been out of training for centuries.
King Kai- Living in the 'Next Dimension,' King Kai is known throughout the universe as one of the greatest fighters and martial arts teachers (although his teaching methods are rather unorthodox).