He was first introduced on Planet Namek when Zarbon and Dodoria (Freeza's henchmen) attacked his village. Dodoria killed everyone in his village, and was about to kill him when Son Gohan and Kuririn jumped in to save him. He, Gohan, and Kuririn narrowly escaped Dodoria's pursuit, after which he was taken to Bulma's "Capsule House" inside a nearby cave. After the Ginyu Force attacked, Dende summoned the Namekian Dragon, Porunga, for Kuririn and Son Gohan to make their wishes. They used their first wish to revive Piccolo, and they used their second wish to transport Piccolo to Planet Namek. Before they could use their third wish, Vegeta intervened by wishing for immortality, but Saichourou had died at that exact moment, and since he created the dragon balls, they turned to stone and Porunga disappeared.
Dende later helped Kuririn, Son Gohan, Vegeta and Piccolo fight Freeza by healing them when they were injured. He was later killed by Freeza while in his final form when Freeza realized that Dende had the power to heal. Dende, along with all the people killed by Frieza, were later revived by the Earth'sDragon Balls and Dende made the final wish during the Super SaiyanGoku vs. Freeza fight. The original wish was to transport everyone on Namek except for Freeza to Earth, but Goku had wanted to stay and fight Freeza to the end, so the two stayed on Planet Namek, which was nearly at the stage of exploding.
Cell Saga
Dende later appears during the conflict with Cell to serve as Kami of Earth. It was thanks to him that the Dragon Balls were useable during the Cell Games Saga.
Buu Saga
In the Fusion Saga, when Buu escapes from the Hyperbolic Time Chamber and turns everyone on Kami's Lookout into chocolate, Dende is saved when Mr. Popo flings him off the Lookout. Dende is one of the few survivors of Buu's attack. After Buu absorbed Gotenks and Piccolo and fought against Mystic Gohan, Dende stepped in to heal Gohan. Buu noticed this and attempted to kill him, but he was saved by Tenshinhan. He was one of the very few people to witness the Kid Buu battle and the Vegetto vs. Super Buu battle. He appears to form somewhat of a friendship with Mr. Satan in the late Fusion Saga episodes.
Dragon Ball GT
In Dragon Ball GT, he fell for a mind control trick and became one of Bebi's servants for a little bit, but he managed to snap out of it. Later, Dende helps Piccolo open a portal to Hell so Goku can escape. Though it takes Dende a few times to get it right, he eventually succeeds. Dende is presumed to live on as Kami far past the end of GT.