Stien

Stien was a duplicated agent working for the Daleks, he encounted the Doctor and Tegan after they landed due to falling into a time corridor in London 1984, he escaped from the Daleks as he could not take the Dalek conditioning, he become an unwitting ally to the Doctor. He joined the Doctor, when he went to confront and kill Davros who was still on a prison ship. Later when the only option was to destroy the prison ship, Stien was the one who intiated the self destruct. (DW: Resurrection of the Daleks)