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 in 2120 by the Bio-Cellular Institute of Dungeness. (REF:The Brilliant Book 2012) Throughout the 22nd century, it became common use at many industrial facilities and by the military. It was believed that there were ten million Gangers in India alone. (DW: The Rebel Flesh / The Almost People)

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. (DW: The Rebel Flesh)

A similar event to Sheppey 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. Miranda Cleaves and the Ganger of Dicken, who also replaced his original, revealed the event to the press and fought for Gangers' rights. (DW: The Rebel Flesh / The Almost People)

India was one of the first nations to grant Ganger independence. Pressure would lead to Gangers elsewhere gaining independence: people would later marry the Gangers of their deceased spouses and a sitcom called I Live Next Door was created about them (and co-starring a Ganger of the lead actress). (REF: The Brilliant Book 2012)

In the 51st century, the technology still existed. The Church and the Silence created a duplicate of Amy Pond without her 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)

Behind the scenes

 * According to The Brilliant Book 2012, a book that contains non-narrative based information; phobias about Gangers spread, with groups like the 'Fear the Flesh!' hyperweblog.