|“||I cleared the area of innocents, in accordance with your wishes. Do you disagree with my methods?||„|
|~ Android 20 after destroying a city|
Dr. Maki Gero, also known as Android 20, is an evil genius and a brilliant weapons designer behind the criminal organization known as the Red Ribbon Army. He is one of Son Goku's arch enemies (alongside Frieza and King Piccolo) in Dragon Ball Z and Dragon Ball Z Kai as well as the lesser extent the non-canon Dragon Ball GT.
As an android, he can drain energy from people through a device on his hand. Being the the one responsible for creating the androids and Cell, as well as Super 17, he is the major antagonist of the Android Saga alongside Cell in Dragon Ball Z and the Super 17 Saga in Dragon Ball GT alongside Super 17 and Dr. Myuu.
Maki Gero was the chief scientist of the Red Ribbon Army (though he is never seen at the time) that created the first androids in the service of the Red Ribbon Army. In the anime, a Dr. Flappe (who looks nothing like Dr. Gero) is named as Android 8's creator. A possible explanation is that Flappe and Gero were partners and constructed the first androids together (most likely including Android 8) or that Flappe merely constructed Android 8 while Gero produced the blueprints and forced him to create him (most likely the latter as Flappe was hinted at being a Red Ribbon member against his own will).Akira confirmed them to be parners and he modeled Android 16 after his late son who was a high-ranking member who died at a gun fire.
After the Red Ribbon Army was defeated by Son Goku, Gero went into hiding in a mountain area that was north of North City where his laboratory was located. In this lab, he strived to create the ultimate fighting machine. Using an extremely intelligent tracking device disguised as a ladybug, he studied Goku and the Z Warriors for years on end: the fights Goku had with Tenshinhan, Piccolo Daimao, Piccolo, and the Saiyans, Raditz, Nappa and Vegeta.
Dr. Gero ceased the study of Goku's power when the Saiyan left for Planet Namek, believing he had already compiled enough information; so he simply adjusted the androids' power levels to accommodate for Goku's expected power increase, not accounting for the power level of Goku's Super Saiyan form. Believing he had created the ultimate fighting machines, he finalized his plans and constructed a series of Artificial Humans (Androids).
Dragon Ball ZDr. Gero sought revenge on Son Goku, so he studied Goku and all his fights on Earth, including his fight with Nappa and Vegeta. He built androids with as much power as an army so they could defeat Goku. It is said by Trunks that the androids killed Dr. Gero when they awakened (as this was what happened in his timeline). However, this did not immediately happen, as Gero awakened Android 19, who made him into Android 20. They attacked a city where Goku and the other Z Fighters (minus Vegeta and Chaozu) were waiting for them. #20 destroyed a city to prevent the people from getting in the way of their fight. In a deserted area, #20 sent #19 after Goku, who then became crippled with a heart virus, and was forced to leave with Yamcha. After Vegeta arrived and destroyed #19, #20 ran, deciding to steal energy from the other Z Fighters so he would be strong enough to defeat Vegeta. He targeted Piccolo first, but Son Gohan stopped him, and Piccolo beat up #20, cutting off his hand. However, Trunks showed up and revealed that #19 and #20 were not the androids from his timeline, but Artificial Humans 17 and 18 were. #20 retreated to his lab, but attacked a man along the way who shot at him mistaking him for a deer, leading Kuririn to fight him. They followed him to his lab where he awakened #17 and #18, who disliked being controlled and took his remote and crushed it. #20 tried to stop #17 and #18 awakening Android 16, saying it was too dangerous to awaken him. #17 then impaled him with his hand surprising everyone, and kicked his head off. He survived, so #17 stomped on his head, crushing it.
Dr. Gero's master computer was creating an ultimate android Cell from the cells of Goku, Son Gohan, Piccolo, Yamcha, Tenshinhan, Chaozu, Vegeta, Nappa, Freeza, and King Cold, which Gero had extracted using an insect-like device. In Cell's timeline (and possibly Trunks' timeline as well), Gero was killed when #17 cut his head off and #18 destroyed his head after he said Cell would swallow them up. In the regular timeline, the master computer and Cell in his larval form were destroyed by Kuririn and Trunks.
He later appeared in Hell alongside several other dead villains during the Pure Boo Saga, watching Goku's fight with Pure Majin Boo.
He also appeared in the movie Super Android 13, during his death at the hands of Android 17 (though the dialogue is changed), with his master computer programmed to think it was Dr. Gero, and it finished building Androids 13, 14, and 15. In the anime (as most of the movies are non-canon) it is said by 18 that all androids up to 15 were destroyed by Gero (excluding Android 8, as Gero never built him).
Dragon Ball GTDr. Gero and Dr. Myuu worked together to build another Android 17 in Hell, brainwashing the original #17 (who was no longer evil) to open up a portal from Hell which most of the dead villains escaped. The two 17s fused together into Super 17. Gero was betrayed and killed by Super 17 with an energy wave.