Seb
The Doctor's TARDISSeb was an interface who worked for Missy in what he liked to call the Nethersphere. He welcomed Matthew, a Shoreditch policeman who was killed by a Skovox Blitzer, as Missy was busy at that time. (TV: The Caretaker)
He also welcomed Danny Pink to the Nethersphere. He offered the man coffee and asked if he had arranged to be cremated. Seb told Danny that he had died, and that he could still feel his body, even though his consciousness was no longer a part of it. He also arranged a meeting between Danny and a boy he had once killed while on duty. When the boy fled during the meeting, Seb told Danny to allow him to leave.
Seb allowed Danny to talk to Clara Oswald, after the latter had, quite "rarely" in his opinion, managed to call Danny. He watched as the two talked, and Danny broke down after Clara ended the call. Seb then gave him the chance to delete his emotions, leaving him alone to make the decision. (TV: Dark Water)
He was next seen in the Nethersphere with Danny and the boy he killed stating that now the dead were going back home as all the lights in the Nethersphere turned off. After that, he appeared in the Nethersphere with Missy watching the Doctor and the Tardis free falling from a plane. He shows clear signs of being impressed when the Doctor manages to open the Tardis and asks for permission to "squeee-" after which Missy casually kills him. It is stated that he is an AI interface when Missy asked him to delete his opinions.(TV: Death in Heaven)
