Cass Fermazzi

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

Cass had already teleported the rest of the crew off the ship when she encountered the Eighth Doctor, whose TARDIS had just materialised onboard. Recognising the Doctor as a Time Lord, Cass chose death over involvement with the Last Great Time War, despite the Doctor's protestations that he wasn't part of the war.

Her death inspired the Doctor to finally take part in the war. (TV: The Night of the Doctor)