Goku and the Z Fighters have tangled against many mad scientists across the entire Dragon Ball mythos but none have loomed as sinisterly large as Doctor Gero. A member of the Red Ribbon Army particularly gifted in advanced robotics, Gero swore revenge on Goku after the Saiyan hero completely dismantled the criminal organization in the original series. By the events of the sequel anime series Dragon Ball Z, Gero had built a squad of powerful androids specifically programmed to kill Goku and anyone who would dare stand in their way, while transferring his own consciousness to a formidable android body.

While Gero himself does not appear in the popular fighting game Dragon Ball FighterZ, set during the events of Dragon Ball Super long after the scientist's destruction at the hands of his own creations, his legacy is felt throughout the game's story mode. A new antagonist bearing the Red Ribbon Army's insignia named Android 21 is introduced in the game, featuring data and DNA from all the Z Fighters and their greatest villains, include Majin Buu, spliced into her genetic makeup as the ultimate synthesis between organics and robotics. As the story mode continues and Android 21 reveals her enigmatic past, the most shocking revelation of all is that she was once in a romantic relationship with Gero.

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While both Android 21 and Gero were still human and working for the Red Ribbon Army, they two were married and had a son together named Gebo whom they designed Android 16 after. This is corroborated by a passing comment made in Dragon Ball Z that Gero had based Android 16 after his dead son, a young Red Ribbon soldier who was killed by an unidentified enemy soldier. To honor his son, Gero implanted Gebo's personality in the android, which ultimately made the resulting creation far more peaceful than Gero had intended, with 16 only agreeing to fight Goku and Cell after the latter became a threat for Earth's natural environment that 16 had grown to love.

The identity of Gero's wife had been a mystery for the entirety of the franchise. While Dragon Ball FighterZ is technically not regarded as canon, the addition of Android 21 in the game's story potentially ties up the long-dangling plot thread. In FighterZ's story mode, Android 21 repairs Android 16 and restores his programming to be even closer to the personality of Gebo. The new and improved 16 attempts to keep his mother's dark side in check before she unintentionally kills him, resulting in a schism between her two personas. Spurred by 16's death, the Z Fighters rally together to destroy the evil Android 21 setting the stage for the game's climactic showdown.

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Android 21's backstory is among the most tragic in Dragon Ball, a human scientist who tragically lost her son to the horrors of war and attempted to resurrect him through robotic means. As her husband became consumed by his thirst for revenge, Android 21 would lose her own humanity as the Red Ribbon Army transformed her into an android while Gero similarly underwent the terrifying transformation. And while 21 and her son would eventually be reunited in their new, robotic forms, 21's programming led her down a dark, vengeful path like her husband resulting in her taking 16's life before destroying herself.

While the character's placement in canon is unclear, Android 21 was designed by franchise creator Akira Toriyama, who also served as a creative consultant on the game's story. As such, it's fair to assume Toriyama does consider her to be Doctor Gero's mystery wife and the mother to their son.

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