Androids

Androids (人造人間, Jinzōningen; lit. "Artificial Humans") are robotic/cyborg Humans, most of which were created by the evil scientist Dr. Gero. Most of the androids are said to have unlimited energy and eternal life. Due to their inorganic nature, they, or at least the ones created by Dr. Gero, also have no detectable aura (unlike Saiyans, Humans, and others), so they cannot be directly tracked using Scouters or Ki Sense.

BackGround
Androids serve as main villains during the Android conflict, each serving a purpose of their own. Originally, all of the androids were plans used to kill Goku, however, most of the androids turn to the good side or are destroyed. However, in Future Trunks' Alternate Timeline, the androids succeed in their plans for world destruction, managing to kill all of the main Z Fighters(except for Goku, who dies of a heart virus, and Gohan, who survives but is killed 13 years later) until finally being destroyed by Trunks almost 20 years later. In DBRII there are very little androids and have no major effect to the story. In DBRI they played a very big part, as several villains were androids, as-well as an anti-hero being an android.