Direct answer: Dr. Gero kidnapped the twin siblings (Lapis and Lazuli) and cybernetically converted them into Androids 17 and 18—he implanted mechanical/cybernetic enhancements, erased or altered memories, put them in stasis when they were hard to control, and later awakened them as part of his plan to create powerful fighters to kill Goku.

Quick facts

  • Victims: the twins later known as Android 17 (Lapis) and Android 18 (Lazuli).
  • Method: kidnapped as children, fitted with cybernetic/artificial-human modifications (making them “androids” in the series sense), and had their memories altered/erased.
  • Motivation: Gero wanted unstoppable warriors to defeat Goku (revenge for the Red Ribbon Army’s defeat) and to study twin subjects for comparative data to refine his designs.
  • Control problems: Gero found them difficult to control, put them into stasis, and later created other androids (19, 20, etc.) and even transferred his brain into an android body when needed. The awakened 17 immediately killed Gero.

Short narrative (how it happened)

  1. Encounter and abduction: Gero met the twins and decided they were ideal subjects, so he abducted them.
  1. Cybernetic conversion: He modified their bodies with cybernetic enhancements—making them “artificial humans” rather than fully synthetic robots—and altered their memories to suit his experiments.
  1. Testing and stasis: Because he couldn’t fully control them (they resisted or behaved unpredictably), he placed them in stasis while continuing work on other androids.
  1. Awakening and consequence: In the Android Saga he is forced to awaken them; Android 17 kills him soon after reactivation.

A brief technical note on terminology

  • “Android” in Dragon Ball often means a cyborg/artificial human (biological humans with cybernetic modifications), not a fully synthetic being; 17 and 18 are modified humans rather than purely mechanical constructs.

If you want

  • I can provide scene-by-scene references (chapters/episodes) that show each step, or a timeline table of events from Gero’s lab to their awakening.

Information gathered from public sources and fandom references.