Martha Jones (clone)

Martha Jones was cloned from the original Martha Jones in order to help the Sontarans to start a war with Earth. As her first job was to deactivate the missiles that UNIT sent to the Sontaran Ship. She then assisted the doctor (Unknown to him that she was a clone). And she tried to stop him from going to the room with the Cloning Pool. But he found out that she was a clone and woke the original Martha up. This broke the link between them and clone Martha died in front of Martha. (DW: The Sontaran Stratagem/The Poison Sky)