In the Manga / Anime
Kami is the Guardian of the Earth and first appears in the original Dragon Ball series. After the evil King Piccolo wished for eternal youth, destroyed Shenron and Goku’s friends, including Krillin, Goku was determined to destroy King Piccolo. Goku eventually kills King Piccolo and climbs up Korin’s Tower to find Kami on top, the top being called Kami’s Lookout. Kami is the only person who has the powers to resurrect Shenron, revealing that the reason King Piccolo was able to kill the dragon in the first place was because they were once the same being. Goku reached Kami’s Lookout and Kami resurrected Shenron on the condition that Goku would train with him over the next 3 years to prepare for the arrival of Piccolo Jr., Goku accepted. Kami took Goku under his wing and taught him everything he knew in the ways of fighting and used unique training methods such as wearing weighted clothing to increase his speed and power.
Three years passed and the 23 World Martial Arts Tournament was underway. Goku and his friends all entered, as well as Piccolo and Kami in disguise. In order to keep his identity secret Kami possessed a weak human and went under the name as Hero. Kami ended up fighting Piccolo and although appearing to have the upper hand with the Evil Containment Wave once used to trap King Piccolo the move was reversed and Kami was than trapped for most of the tournament inside a bottle. He is freed during the final battle of the tournament when Goku grabs the bottle from Piccolo and sets Kami free. Seeing Goku defeat Piccolo, and show compassion by giving him a Senzu Bean after the fight, Kami offers Goku his role of Guardian of the Earth. Goku politely declines and flies off with his future bride Chi Chi.
Kami, although in the background and never really fighting, plays a key role in Dragon Ball Z from the very start. When Goku is killed in the battle with Raditz Kami recommends Goku to receive special training in other world from the all-powerful King Kai. His request is heard and accepted. Later in the battle with Nappa and Vegeta Piccolo is killed and since Kami and Piccolo are one and the same he too dies and the dragon balls turn to stone.
During the struggle on Namek Kami is brought back with the Namekian dragon balls and with him being alive the earth’s dragon balls are restored to their original power. He uses the dragon balls to bring everyone on Namek to earth, except for Goku and Frieza.
Kami is last seen in Dragon Ball Z when the Androids are attacking. Piccolo is worried that not even Goku can beat them so he travels to Kami’s Lookout in order to merge with Kami. Kami is reluctant at first but realizes Piccolo has changed to the side of good and merges with him, making Piccolo significantly more powerful and giving all his knowledge to Piccolo.
In the Video Games
Kami is not a playable character or fighter in any of the Dragon Ball games but does play a role in the story or as a character of guidance.