The Kai (Kai) are upper-level gods of the Dragon Ball universe. There are five at a time that rule over the main galaxy of the universe, with one presiding over each of the four quadrants in a galaxy, and the last overseeing them all. The Kai are responsible for the lower-level gods, who rule over individual planets. The Kai reside in the heavens, with each having their own small planet. There is a sense of competition among the Kai over whose quadrant has the best fighters. King Kai, the Northern Kai, trains Goku after his self-sacrifice to defeat Raditz.

King Kai, also known as Lord of the Worlds (Kaiō-sama) and North Kai (Kita no Kaiō), is the Kai of the northern quadrant of the galaxy. His companion is a pet monkey named Bubbles and in the anime he also has a flying cricket companion named Gregory. King Kai trains fighters allowed to keep their bodies if they manage to reach his small planet at the end of Snake Way. Before training any students, he forces them to appeal to his strange sense of humor, catch Bubbles, and hit Gregory with a mallet. He provides Goku with martial arts training and two of his own techniques, the Genki Dama and the Kaio-ken, which King Kai was never able to master. He continues to help Goku and his friends throughout the series, lending his planet locating and telecommunicating abilities for their use. When Goku brings a self-destructing Cell to his planet, the explosion kills King Kai and destroys his planet. As he is already in the Other World, he only gains a halo and in the anime he appears to settle down on Grand Kai's planet.