Dr. Gero made himself into a cyborg by implanting his brain into a robot body. He first appeared with Android #19 to kill Goku. After #19 was destroyed by Vegeta, he fled out of fear and with the intention of activating Android #17 and #18. Once he activated them, they quickly rebelled on their creator. #17 kicked his head off and crushed it.
After the Red Ribbon Army was defeated by Goku, Dr. Gero goes into hiding in his laboratory located in a mountain area north of North City. In this lab, he strives to create the ultimate fighting machine. Using an extremely intelligent tracking device disguised as a ladybug, he studies Goku and the Z Fighters for years, observing the fights Goku has with Tien Shinhan, King Piccolo, Piccolo, and the Saiyans Raditz, Nappa and Vegeta.
Dr. Gero ceases the study of Goku's power when the Saiyan leaves for Namek, believing he had already compiled enough information; so he simply adjusts 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 finalizes his plans and constructed a series of Androids. Android 16 was modeled on Gero's dead son, a high-ranking Red Ribbon soldier long ago felled by an enemy bullet. In his affection, Gero made him powerful, but did not want him to be destroyed in battle, so he made him gentle. While looking for fresh material for his experiments, Dr. Gero meets two notorious delinquents by chance, two siblings, a boy and a girl. He then kidnaps them and restructures them into Android 17 and Android 18. However, the two became rebellious as they retain their human free will, so he deactivated them.
