The episode marked Eccleston's first appearance as the Doctor, succeeding several other actors who played the role, and Piper's debut as the Doctor's travelling companion Rose. Being the first episode of the revived series, several recurring characters were introduced: Camille Coduri as Jackie Tyler, and Noel Clarke as Mickey Smith. Viewers did not see the Doctor character regenerate from a previous incarnation, regeneration being a plot device in which the character of the Doctor changes appearance. Russell T Davies felt it would be clearer for the viewer to begin the series with the new actor in place rather than show the previous actor regenerating.