As a franchise focused heavily on martial arts, Dragon Ball has featured a whole host of trainers and teachers as the main characters constantly work towards new levels of strength and power. Dragon Ball Z introduced one of the strangest, most masterful teachers in King Kai, Goku's first mentor in the anime follow-up to Dragon Ball.
Residing in the franchise's version of the afterlife, the first Kai made the Dragon Ball protagonist exponentially stronger despite his off-kilter, comical teaching style and gave Goku several techniques that the Saiyan hero would rely on for years to come. Since then, King Kai would continue to appear in Z and its subsequent sequel series, including Dragon Ball Super, along with many of the franchise's animated films. As such a pivotal character, here's an overview on Goku's first teacher from Z.
Origins of the Kai
King Kai's existence is first mentioned by Kami, Goku's teacher at the end of Dragon Ball and the Guardian of Earth, at the start of Dragon Ball Z. The elder Namekian is escorting the recently deceased Goku into the afterlife to train for the arrival of new villains Vegeta and Nappa in a year's time and receives permission from King Yemma, the gatekeeper of the afterlife, to send Goku on Snake Way to receive training from King Kai.
After running down the winding, serpentine road above the clouds, Goku finds King Kai's small planet hovering above the end of Snake Way. Upon leaping onto it, Goku quickly discovers the gravitational pull of the dense planet is five times greater than that of Earth, greatly weighing him down. He is then greeted by King Kai, the godly figure resembling a short, portly blue cockroach, and his two companions: a chimpanzee named Bubbles and a floating grasshopper named Gregory. Upon their first meeting, King Kai agrees to train Goku, but only if the Saiyan can make him laugh, which he eventually does.
King Kai's initial training has Goku try to catch Bubbles to grow accustomed to the planet's augmented gravity and later try to wallop Gregory with a heavy hammer to boost Goku's base strength. Upon completion of both seemingly menial tasks, King Kai teaches his newest student the Kaio Ken technique, allowing Goku to temporarily push his body beyond its natural limits of power, and the Spirit Bomb, which has Goku gather energy from everything around him to form a powerful blast. Both techniques become staples for the remainder of the franchise and prove invaluable.
Following Goku's resurrection and return to Earth, King Kai later trains Tien, Yamcha and Chiaotzu after their own deaths fighting the Saiyans. While King Kai does not teach them either the Kaio Ken technique or Spirit Bomb, all three fighters' powers are significantly increased by the training. Piccolo is similarly offered a chance to train under King Kai but refuses to indulge the afterlife figure's antics.
King Kai's Legacy
In a last ditch effort to save the Earth from Cell, Goku teleports the villain to King Kai's planet moments before the villain self-destructs, killing everyone on the small world. Fortunately, King Kai and his friends instantly reappear in the afterlife, completely unfazed by their explosive deaths. It is then that King Kai reveals to Goku that he is only in charge of overseeing a single quadrant of the universe and introduces him to his three counterparts. Additionally, King Kai has Goku meet his direct superior, the Grand Kai. While an even higher Kai, the Supreme Kai reveals himself to Goku and his friends years later, surprising even King Kai about his existence.
While King Kai only taught Goku for several months and is never seen training any new fighters after the resurrection of Tien, Yamcha and Chiaotzu, his legacy remains. A source of comedic relief, advice and insight to the Z Fighters as they encounter increasingly powerful new enemies, King Kai is wise, even if his appearance and demeanor are hard to take seriously.
Dragon Ball Super Volume 7 is out on Blu-ray now.