Ganger

Gangers, shortened from "Doppelgängers", were a clone race created by humans from an artificially created organic substance called the Flesh.

Biology
Gangers were mimicked duplicates of individual humans who controlled their Gangers through telepathic remote control via a specially-designed harness. This allowed humans to work in extremely hostile environments without risk to themselves, as the Gangers could be easily recreated and any damage they sustained would not be felt by the real human as the nerve endings automatically shut down.

It has been shown that, in at least one case, that Gangers exhibited the ability to extend their limbs and neck, due to the unstable molecules of the Flesh material.

The Gangers are mostly unstable and shift between half-Flesh and full human faces which was said to be hard to maintain, at least the early ones did, though the Amy and Melody Pond Gangers didn't experience this, but it was indicated they were a more advanced version so this flaw may have been corrected later on. Exposure to the inside of a TARDIS stabalized a Ganger and made them fully human.

History
The Ganger process was developed some time during the 22nd century, and was in common use at many industrial facilities. It was believed that there were ten million Gangers in India alone.

Those working with Gangers talked of an incident at the Isle of Sheppey, in which a Ganger was electrocuted, resulting in the Ganger gaining sentience and horrifically killing its operator. A similar event occurred at St. John's Monastery, an acid-mining facility that used Gangers. After the facility was hit by a solar storm, the active Gangers gained independent thought and motion, being implanted with the memories of their templates and becoming increasingly fixated on the possibility of making their own lives. This possibility became a reality for the Ganger of Jimmy after the death of his predecessor and the Ganger of Dicken.

Although Miranda Cleaves and the Ganger of Dicken, who also replaced his original, fought for Gangers' rights, the technology was still used on people such as Amy Pond to create duplicates without their knowledge. (DW: The Rebel Flesh / The Almost People) A Ganger of Melody Pond was also created to fool Amy and the Doctor. (DW: A Good Man Goes to War)