Tarkin

After attending the American premiere of the first Star Wars film, the Sixth Doctor remarked that the actor who played Tarkin looked familiar, and seemed to recall meeting his granddaughter. (AUDIO: Mission: Impractical)

Behind the scenes
Grand Moff Tarkin was played by Peter Cushing, who also played Dr. Who in Dr. Who and the Daleks and Daleks' Invasion Earth 2150 A.D.. The granddaughter in question is Susan.