From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Kaios originally come from Planet Kaishin located in the Kaioshin Realm. The planet was basically a larger version of the planets that the four Kaios called home (such as North Kaio's World). On the planet were gigantic trees called Kaiju, and the Kaios were all born from the fruit of this tree as Shins. The population of this planet was roughly about 80 or so. The Shins were genderless and their average life expectancy was said to be 75,000 years. They lived leisurely lives, studying various things at a school-like castle. Whenever one of the Kaios in the Next World died, they drew lots among themselves to choose who would take that Kaio's place and become the new Kaio. The Kaioshins, however, were chosen only from among Shin born from a special golden fruit that was particularly rare. Occasionally, there were delinquent Shins with evil hearts whom became Makaios (Demon Realm Kings) and Makaioshins (Gods of the Demon Realm Kings).
The Kaios ruled over the four galaxies of the Mortal Realm, with each Kaio ruling over one galaxy. Their job was to watch over their galaxy and oversee the Kami of their respective planets. The four Kaios were North Kaio, South Kaio, East Kaio, and West Kaio. Grand Kaio was their superior and oversaw over the entire macrocosm.
Above the Kaios were the Kaioshins who not only ruled over the four galaxies of the Mortal Realm, one for each galaxy, but also the four quadrants of the Next World. A Grand Kaioshin was their superior and ruled over the entire Mortal Realm and Next World.
The Kaios lived in the Next World. It should be noted that they are among the few living residents in the Next World. They were considered immortal in the sense that they refered to residents of the Mortal Realm as "mortals", but could still die of unnatural causes (as North did when he was inadvertently killed by the self-destructing Cell). Since they were already in the Next World, it did not really affect them in the long run, however, North Kaio did receive tons of laughter and bullying from his fellow Kaios for being dead. The Kaios were also known to have a love for fancy cars and each Kaio owned one.
During the events in the series, the Kaios proved not to be strong enough to oppose the villains directly, though they seemed to influence the process by giving wise advice or providing training. North Kaio had amazingly powerful Telepathy skills, being able to transfer his thoughts to whole planets or even galaxies, and he also taught Goku highly useful techniques such as the Spirit Bomb and Kaio-ken techniques.
In Dragon Ball Z: Bojack Unbound, North Kaio explained that in the past, he and the other three Kaios (South, East, and West) took it upon themselves to stop the evil galactic thug Bojack. To do so, they combined their power and imprisoned Bojack and his followers in a planet (a star in the dub) at the far end of the galaxy. Bojack and his henchmen were later set free when North Kaio's World was destroyed and North Kaio was killed by the self-destructing Cell, causing the seal which bound Bojack to break.
- 界 = World
- 王 = King
- Every Kaio wears some form of eyewear.
- South Kaio and North Kaio are the only Kaios ever shown in the manga.