All of the Kaioshin were originally born on the Planet Kaishin as Shin-jin. When the Kaiju trees grew incredibly rare golden fruit, this meant that a Kaioshin would be born. Unlike the normal Shin-jin, who could later possibly become normal Kai, the Shin-jin born from the special gold fruit had far more power and longer lifespans, up to millions of years longer than the average member of their race, whose lifespans are around 75,000 years.
Protectors of the Universe
Each of the Supreme Kais once ruled over a quadrant of the entire universe, with a Grand Supreme Kai overseeing them and who ruled over the entire universe (the same way that regular Kais are the highest gods of their individual quadrants of a galaxy, with a Grand Kai in charge of the four of them). Each Supreme Kai oversaw the regular Kais in his/her quadrant of the universe.
According to the Eastern Supreme Kai, each of them were a thousand times more powerful than Frieza, but all except for him and Lila were killed or absorbed by Majin Buu in 5 Million Before Age, resulting in the mindless killing machine seen in the first two forms of Buu being "tamed" into becoming the innocuous fat Majin Buu.
Like the regular Kais, the Supreme Kais are among the few living residents in Other World. They can still die; however, since they are already in Other World, it doesn't really affect them in the long run, unless they are somehow obliterated or absorbed. Unlike regular Kais, who, like the North Kai, had to visit King Yemma after his death, Kais like the Old Kai also received halos after death, but were never forced to visit the giant ogre. This is likely due to the incredible supremacy such Kais have over the lowly ogre in comparison.