Karlax

Karlax was a Time Lord on the High Council during the Last Great Time War. He had a history with the Doctor, and hated him because of it.

When the War Doctor arrived on Gallifrey to show Rassilon and the High Council of a new Dalek plot to wipe Gallifrey from history, Karlax and the Castellan kidnapped the Doctor's companion, Cinder and exposed her to a mind probe.

When the Doctor escaped his imprisonment on Gallifrey, Karlax pursued him with some help from the Celestial Intervention Agency. When the CIA and their Battle TARDISes were attacked by Dalek stealth ships, the Doctor materialised around Karlax and saved him from death, at the cost of him regenerating. The Doctor and Cinder took Karlax to the TARDIS' Zero Room where he could recover.

Karlax regained consciousness and attempted to take the Doctor's TARDIS back to Gallfrey. The Doctor planned for Karlax's deception and set the TARDIS controls to make it dematerialise around the Doctor if Karlax tried to pilot it. Realising he had been tricked, Karlax shot Cinder by means of enacting some revenge on the Doctor. He then tried to take over the TARDIS. The Doctor dematerialised his TARDIS, setting the controls so that Karlax would be left behind in the middle of the Dalek Eternity Circle. (PROSE: Engines of War)