From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Doctor Gero (ドクター ゲロ, Dokutā Gero; FUNimation "Dr. Gero", Viz "Dr. Gero"), later known as Artificial Human No. 20 (人造 人間 20号, Jinzō Ningen Nijū-Gō; FUNimation "Android 20", Viz "Android #20"), is a mad scientist who works for the Red Ribbon Army. After the army's defeat by the hands of Son Goku, Gero retreats to his mountain laboratory to plot his revenge with his Artificial Humans. Not until he reaches Artificial Human No. 19 does he create an obedient, bloodthirsty servant. Gero then has No. 19 transplant his own Human brain into an Artificial Human body, thus turning himself into No. 20 and preventing death by old age. After his second defeat at the hands of the Z Warriors, Gero retreats to his lab to activate Artificial Human No. 17 and Artificial Human No. 18, who soon rebel and kill their creator. Though Gero dies, he leaves behind Artificial Human No. 13, Artificial Human No. 14, Artificial Human No. 15, and his ultimate creation, Cell.
Quest for vengeance
Gero was the head scientist for the Red Ribbon Army, although he was never seen at the time. He created the first Artificial Human 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 Metro North where his laboratory was located. In this lab, he strived to create the ultimate fighting machine. Using an extremely intelligent spy robot disguised as a ladybug, he studied Goku and Planet Earth's warriors year after year.
In the anime, a Prof. Frappe, who looks nothing like Gero, was named as the creator of Artificial Human No. 8. A possible explanation is that Frappe and Gero were partners and constructed the first Artificial Humans together, most likely including No. 8, or that Frappe merely constructed No. 8 while Gero produced the blueprints and forced Frappe to create him (most likely the latter, as he was hinted at being a RR member against his own will).
Artificial Humans unleashed
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. He simply adjusted the Artificial Humand' battle powers 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 Artificial Humans.
A year after the destruction of Planet Namek, the Z Warriors received a tip from Future Trunks Brief that two extremely powerful Artificial Humans would appear shortly. Three years later, on May 12th, 10:00 AM on an island nine miles southwest of Metro South, two Artificial Humans appeared – No. 19 and No. 20. Together, they killed many people including a man who had his head ripped off by No. 20. Yamucha was the first to confront them since they were attracted by his battle power.
Before Yamucha could act, No. 20 demonstrated a deadly power. Gero's latest design for Artificial Humans included an energy absorbing function. Using a small red jewel embedded in his hand, he grabbed Yamucha by the jaw, punched a hole through his body, and sapped his life force. After an explanation of their origins to Goku, Tenshinhan, and Piccolo, No. 20 destroyed half of the city. Goku led him and No. 19 out of the city to avoid killing more people in the fight. On some unknown island, No. 20 began to explain to Goku that Gero had wanted revenge on Goku for destroying the Red Ribbon Army. After the explanation, he ordered No. 19 to fight Goku. Due to the Saiyan's Heart Virus that manifested at that exact moment, No. 19 won. After Vegeta defeated No. 19, No. 20 ran away.
During the ensuing search, No. 20 attacked Piccolo from behind, only to be foiled by Son Gohan. He tried to fight Piccolo head-on, but Piccolo was superior by far as a result of three years of intense training with Goku (and probably also the Fusion with Nail). Piccolo mercilessly severed the Artificial Human's arm and prepared to destroy him when he (the Artificial Human) retreated once again into the rocky mountains. No. 20 decided to retreat to Doctor Gero's Laboratory in order to activate Artificial Human No. 17 and Artificial Human No. 18. Bulma Brief, having recognized him, notified the Z Warriors about the approximate area of his laboratory and they departed for the north.
While approaching his lab, No. 20 ambushed Kuririn, but spared him in his hurry to activate the Artificial Humans. Kuririn followed him to his lab and summoned the Z Warriors there. No. 20 entered his lab and activated No. 17 and No. 18, having a controller that could deactivate them in case they rebeled again. The Artificial Humans fooled him into believing they were obedient until they snatched the control from him. After they crushed, they brutally murdered him by severing his head. His remains were later destroyed along with what seemed to be the rest of his laboratory at the hands of Future Trunks when he fired a blast with the intention of destroying No. 17 and No. 18.
During the Imperfect Cell Saga, Gero appeared in a flashback wherein he had begun his creation of Cell. Gero (as a Human) had discovered a way to fuse together the cells from the strongest warriors to walk Earth and create a supreme fighting entity. After realizing that his project would take too long to be completed before his time, he decided to turn attention to other matters and leave his supercomputer to complete Cell. Towards the end of the Cell Games Saga, Gero (in the form of No. 20) appeared in Super Perfect Cell's flashback again where he was killed as he finished off the settings for the supercomputer to begin working on completing Cell (which contradicted his previous statement that Gero had abandoned the project).
Gero was not seen again until the final anime-filler segments in "Vegeta's Respect". By means unknown, Gero had been permitted by Great King Yama to keep his Artificial Human body while entering Hell. Along with Super Perfect Cell, Freeza, King Cold, and the Ginyu Force, Gero watched the final battle between Goku and Kid Boo. He was one of the very few people cheering for Kid Boo.
Escape from Hell
Dr. Gero is first seen in Dragon Ball GT in Hell along with Dr. Myu. There, they worked on a plan to create the ultimate android which could destroy Goku. They came up with a plan to combine both of their technologies and get a perfect Android by fusing Android 17 and Hell Fighter 17 to create Super 17. They then created a dimensional hole to get both Androids in the same place - Earth. During the fight with the Saiyans, he is betrayed by Dr. Myu who commanded Super 17 to kill him, leading to his somewhat ironic death (killed by Android 17 again). Dr. Gero was later sent back to Hell.
- In the present timeline, Android 17 impales Gero with his hand and kicks his head off, then crushes it like a bug.
- In Future Trunks' and Future Cell's timeline, Android 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 Dragon Ball GT, Super 17 launches an energy wave that blasts Gero into pieces. This is when he dies for the second time in the present timeline.
- Dragon Ball Z: The Legend
- Dragon Ball Z: The Legacy of Goku II
- Dragon Ball Z: Supersonic Warriors
- Dragon Ball GT: Transformation
- Dragon Ball Z: Budokai 2
- Dragon Ball Z: Budokai 3
- Dragon Ball Z: Budokai Tenkaichi
- Dragon Ball Z: Budokai Tenkaichi 2
- Dragon Ball Z: Budokai Tenkaichi 3
- Dragon Ball Z: Infinite World
- Dragon Ball: Raging Blast
- Dragon Ball: Raging Blast 2
Aside from his incredible intelligence (one of the best in the world, impressing even Capsule Corporation president Dr. Brief), Gero has gained combat abilities due to placing his own brain into an energy-absorbing model Android.
- Energy Attack
- Sāchi Shisutemu – Built into his own body is a Sāchi Shisutemu (サーチ システム, Sāchi Shisutemu; Literally meaning "Search System") that allows Gero to detect energy levels.
- Energy Absorption – 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.
- Pesky Fly – A rush attack Gero uses against Krillin.
- Bionic Punisher – A powerful beam shot from both his eyes, which is strong enough to devastate an entire city, or pierce through someone.
- Finish Sign – A power up move that Gero uses in Dragon Ball: Raging Blast.
- False Courage – A power up move that Gero uses in Raging Blast.
- Full Power Energy Wave – Gero uses this attack in Raging Blast.
- Japanese dub: Kōji Yada
- Ocean Group dub: Brian Dobson
- Blue Water dub: Jonathan Love (DBGT)
- FUNimation dub: Kent Williams
- German dub: Gerhard Paul
- Italian dub: Oliviero Corbetta
- Portuguese dub: António Semedo
- Brazilian dub: Aldo César (DBZ), Luis Carlos de Moraes (DBGT)
- According to "Laboratory Basement", one of Gero's ventures outside of cybernetics included plans for a gas-powered toaster oven.
- In both Super Android 13 and the brief flashback in Dragon Ball GT, the dialog in which No. 17 kills him is different than that of the Dragon Ball Z anime.
- The only Human part of him as an Android is his brain, which is transplanted into him by No. 19.
- An interesting point is that Gero transferred his own brain into an energy-absorbing model Android rather than an infinite-powered one like No. 17 and No. 18, which would allow him far greater power reserves that surpasses untrained Super Saiyans. This would make Gero weaker than No. 17 and No. 18. Why he chose to be an energy-absorber rather than an infinite-power Android is unknown (though 18 hints that it may have been because he thought that an energy-absorbing model Android was easier to use as a host).
- In Trunks' "flashback" on Gero's creation of the Androids, one of them killed him by smashing his brain with their hand.
- In the FUNimation dub, the 'G' in his name is pronounced like a soft 'J' and the 'er' is pronounced as such. In the Ocean Group dub, they start pronouncing it differently with the 'G' sounding like a hard 'J' and the 'ero' sounding more like "arrow". In the original Japanese dub and translations that followed this pronunciation, the 'G' in his name is a normal 'G' as in "grip", making his name 'Geh-roh' as in grapple.
- According to No. 18, Gero destroys all of the other Androids up to No. 15 with the exception of No. 8, who was assembled by Flappe in the anime (though the manga states otherwise, leaving no doubt as to who its real creator was).
- Right after Gero activates No. 17 and No. 18, he replies to No. 18's statement, "I see that you have chosen to become an android," by agreeing and saying that he had "eternal life like ." This implies that the process of turning a Human into an Android completely halts their aging, thus making the cyborg immune to at least natural death/illness.
- Despite being part of the Red Ribbon Army, which played a major role in Dragon Ball, Gero was never even mentioned until the Trunks Saga in Dragon Ball Z.
- Contrary to popular belief, the destruction of the Red Ribbon Army was not the primary reason why Gero desired to create Androids and Cyborgs, as he reveals in Dragon Ball GT that he always dreamed of replacing the entire human race with artificial beings even before Goku had defeated the Red Ribbon Army.
- In one flashback sequence from the episode "Double Trouble for Goku", Master Roshi refers to Gero as the "current leader" of the Red Ribbon Army.
- In Dragon Ball Z: Supersonic Warriors, Gero has a what if saga creating androids to try and destroy Goku. Every time he tries, Goku and his friends defeat him and foil his plans forcing Gero to return to his lab defeated.
- In Hell, Gero is seen without his hat when he watches Goku's fight against Kid Boo. Soon afterwards in Dragon Ball GT, Gero is seen with his hat back on.