Cass Fermazzi

Cass was the sole remaining pilot of a space gunship. She died when the ship crash-landed on the planet Karn.

Biography
Cass had already teleported the rest of the crew off the ship when she encountered the Eighth Doctor, whose TARDIS had just materialised onboard. Recognizing the Doctor as a Time Lord, Cass chose death rather than to become involved with the Last Great Time War, despite the Doctor's protestations.

Her death inspired the Doctor to finally take part in the war. (TV: The Night of the Doctor)
 * The reason for her ship's proximity to Karn remains unknown.

Behind the Scenes
Emma Campbell-Jones had previously played Doctor Kent in The Wedding of River Song, also written by Steven Moffat.