Rusty the Dalek

"Rusty" was the name given by the Twelfth Doctor to a Dalek captured by the forces of Combined Galactic Resistance. Intrigued by Rusty's desire to exterminate the Daleks, the Doctor decided to explore the possibility for a "moral Dalek".

Seeing the birth of a star triggered a realisation in Rusty of the inevitability of life returning despite the efforts of the Daleks. The Doctor, Clara Oswald, Journey Blue, Ross and Gretchen Carlisle were shrunk and ventured into Rusty to try to fix the damage that was killing him. Using his sonic screwdriver, the Doctor repaired a crack in Rusty's power source that was leaking radiation and killing him.