Dragon Ball, Dr. Gero is the head scientist of the Red Ribbon Army, though he is never seen at the time. He created the first androids in the service of the Red Ribbon Army. After the Red Ribbon Army was defeated by Goku, he went into hiding. He hid in a mountain area, 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 devices disguised as a ladybug, he studied Goku and Earth's warriors for years on end. In the anime, a Dr. Flappe, who looks nothing like Dr. Gero, is named as the creator of Android 8. A possible explanation is that Dr. Flappe and Dr. Gero were partners and constructed the first androids together, most likely including Android 8, or that Dr. Flappe merely constructed Android 8 while Dr. Gero produced the blueprints and forced Dr. Flappe to create him (most likely the latter, as he was hinted at being a RR member against his own will).
Dr. Gero ceased the study of Goku's power when the Saiyan left for Planet Namek, believing he had already compiled enough information by the Vegeta Saga; so he simply adjusted the androids' power levels to accommodate for Goku's expected power increase, not accounting for the possibility that Goku would become a Super Saiyan. Believing he had created the ultimate fighting machines, he finalized his plans and constructed a series of Androids.A year after the destruction of Namek, the Z Fighters receive a tip from Future Trunks that two extremely powerful Androids will appear shortly. Three years later, on May 12th at 10:00 am, on an island nine miles south-west of South City, two Androids appear: Android 19 and Android 20. Together, they kill many people, including a man who has his head ripped off by Android 20. Yamcha is the first to find them, as they were attracted to his power level. Before Yamcha can act, Android 20 demonstrates a deadly power: Dr. Gero's latest design for Androids included an energy absorbing function. Using a small red jewel embedded in his hand, he grabs Yamcha by the jaw, punches a hole through his body, and saps his life-force. After an explanation of their origins to Goku, Tien and Piccolo, Android 20 single-handedly destroys half of the city. Goku leads him and Android 19 out of the city, to avoid killing more people in the fight. In some unknown island, Android 20 begins to explain to Goku why Gero wants to have his revenge on him for destroying the Red Ribbon Army. After the explanation, he orders Android 19 fight Goku. Due to the Saiyan's heart virus that manifests at that exact moment, Android 19 wins. After Vegeta defeats Android 19, Android 20 retreats. During the ensuing search, Android 20 attacks Piccolo from behind, only to be foiled by Gohan. He tries to fight Piccolo head-on, but Piccolo is superior by far as a result of three years of intense training with Goku (and probably also the fusion with Nail). Piccolo mercilessly severs the android's arm and prepares to destroy him when he (the Android) retreats once again into the rocky mountains. Android 20 decides to retreat into his lab, in order to activate Android 17 and Android 18. Bulma, having recognized him as Dr. Gero, notifies the Z Warriors about the approximate area of his laboratory, and they depart for the north.While approaching his lab, Android 20 ambushes Krillin but spares him in his hurry to activate his Androids. Krillin follows him to his lab and summons the Z Warriors there. Android 20 enters his lab and activates Android 17 and Android 18, having a controller that can deactivate in case they rebel again. The androids fool him into believing their are obedient, until they snatch the control from him. After crushing it, they brutally murder him by severing his head. His remains are later destroyed along with what seems to be the rest of his laboratory at the hands of Future Trunks when he fires a blast with the intention of destroying Android 17 and Android 18.In the Imperfect Cell Saga, Dr. Gero had appeared in the flashback wherein he had begun his creation of Cell. Dr. Gero (in his human form) discovers that his project is taking too long, he then abandoned it so then the supercomputer from the lab begins to complete Cell. Towards the end of the Cell Games Saga, Dr. Gero (in the form of Android 20) appears in Super Perfect Cell's flashback again where he is killed as he finishes off the settings for the supercomputer to to begin working on completing Cell (which contradicts his previous statement that Dr. Gero abandoned it).
Dr. Gero is not seen again until the final anime-filler segments of Dragon Ball Z. By means unknown, Dr. Gero has been permitted by King Yemma to keep his android body while entering Hell. Along with Super Perfect Cell, Frieza, King Cold and the Ginyu Force, Dr. Gero watches the final battle between Goku and Kid Buu, being one of the very few people cheering for Kid Buu.
Aside from his incredible intelligence (one of the best in the world, impressing even Capsule Corp president Dr. Brief), Dr. Gero has gained combat abilities due to placing his own brain into an energy-absorbing model android.
- Energy Attack - The most basic form of energy wave used by androids.
- Built in Scouter - Built into his own Android body is a scouter that allows Gero to detect energy levels.
- Energy Absorption - As an Android, Dr. Gero has special pads on his palms that allows him to absorb life-energy from his victims by grabbing them.
- Photon Wave - From the energy-absorbing pads, he releases a massive wave of explosive energy that can level an entire valley.
- Levitate - Like most characters in the series, Gero can fly in the air. However, like most Androids, he does not possess ki, so he flies by the means of a certain machine called Hikou in his body.
- Bionic Punisher - A powerful beam shot from both his eyes, which is strong enough to devastate an entire city, or pierce through someone.
- In the present timeline, 17 impales with his hand and kicks his head off, then crushes it like a bug.
- In Cell's timeline, 18 distracts him by knocking over some equipment, and 17 cuts his head off. As he warns them about Cell absorbing them, 18 blows up his head.
- In Future Trunks' timeline, 17 and 18 kill Dr. Gero right after they are activated, though it is not explained how. As this timeline is the same one as Cell's timeline at this point, he should have died in the same way mentioned in the previous point.
- In Dragon Ball GT, Super 17 launches an energy wave that blasts Dr. Gero to pieces.