DOCTOR WHO IN DETAIL

Nardole, a humanoid extra-terrestrial, was met by the Twelfth Doctor after becoming decapitated and his head used as a part of the cyborg. The Doctor later re-assembled Nardole joined the Doctor, and helped the Doctor keep his oath to guard a vault at the university the Doctor taught at.

Often staying behind Nardole did sometimes venture off-Earth with the Doctor an Bill Potts including to the Mondassian space craft caught in a black hole on which Nardole stayed to help the remaining Mondassians against the Cybermen.

First regular appearance: The Husbands of River Song

Final regular appearance: The Doctor Falls