From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Gill (ギル, Giru; FUNimation "Giru") is a Machine Mutant.
Dragon ball GT
Gill accompanied Son Goku, Son Pan, and Trunks Brief on their quest to find the Black Star Dragon Balls. He was best friends with Pan, however, he was frequently the recipient of a lot of abuse (both verbal and physical) by her, which made him somewhat fearful of her.
Black Star Dragon Ball Saga
Main article: Black Star Dragon Ball Saga
The three first met him on Planet Imecka and found him on the brink of death. After eating the Dragon Radar for energy, he tried to escape from them. He was ultimately caught by Goku. After that, they found out that the radar had integrated into his software. Upon arriving on Planet M2, he seem to have betrayed the three when he was actually pretending as ordered by Trunks.
Gill was initially programmed to find and lure the Saiyans to the planet in order to use their DNA. Due to a memory failure, he forgot the entire mission until the team neared Planet M2. He then told Trunks the truth of his mission, and together they decided to make the "inhabitants" of the planet believe that Giru was acting according to his programming by giving them data to capture Goku, Pan, and Trunks.
After he set the trio free, they found Dr. Mu's evil creation, Baby, and seemingly destroyed him. Trunks and Goku then finished off Rild, a seemingly unstoppable Machine Mutant who could control metal, and left the planet for good.
Main article: Baby Saga
Upon returning to Earth and discovering that Baby had taken over, Gill attacked Vegeta Baby with a missile only to be "killed" with a single energy blast. Later, Mister Satan and Pan discovered his "corpse" and a grief-stricken Pan took him with them. After Baby's defeat, he was repaired by Trunks.
Super 17 Saga
Main article: Super 17 Saga
During the Super 17 Saga, he restored Son Gohan's legs and left arm back to normal after they were converted to metal by Rild.
Shadow Dragon Saga
Main article: Shadow Dragon Saga
During the Shadow Dragon Saga, Gill went with Goku and Pan to search for the seven Evil Dragons. Gill was fatally damaged by Eis Shen Long, though he was resurrected when Goku made his last wish from Shen Long. It is unknown what happened to him when Goku left for 100 years.
Gill is one of Pan's special attacks in Dragon Ball Z: Budokai Tenkaichi 2 and Dragon Ball Z: Budokai Tenkaichi 3. He also helps Pan with the Dragon Net Battle in Budokai Tenkaichi 3 for the Wii, acting as the lag indicator. He also appeared in Dragon Ball Z: Infinite World in the closing credits and as Pan's special finishing move.
Gill appeared in Dragon Ball GT: Transformation. He aids Pan in attacking the enemy.
For defense, Gill has a small but powerful Rocket Launcher in his chest cavity. He also has the unique ability to reverse General Rild's Metal Breath beam victims via a green beam. After eating the Dragon Radar, the radar itself appears on his back.