Carl Harris

Private Harris is a UNIT soldier. He is first seen ushering in a UNIT Taskforce as they raid the ATMOS complex. During Operation Blue Sky he discovers a cloning vat in the basement of ATMOS. It was there that he was commended for his leadership skills by non other than a Sontaran, General Staal. Staal gave him the promotion he desired as he was hypnotised by the Sontaran to work for them. He and Private Gray later captured Martha Jones in order to have her cloned as well. He was later used alongside Private Gray to teleport the TARDIS to the Sontaran ship, after their jobs had been completed he and Gray were killed by a Sontaran soldier.(DW: The Sontaran Stratagem)

Behind the Scenes
However, on the next time trailer for Turn Left, Private Harris was seen saying the Doctor was dead.
 * This may be a similar-looking person, or either he survived his encounter with the Sontarans. However the episode takes place in the past of an alternate timeline, so Harris is assumed to be still alive in this episode.