The Doctor (Tom Baker) in The Deadly Assassin (1976), Lord President Rassilon (Donald Sumpter) in Hell Bent (2015) and the ruins of Gallifrey during the Time War in The Day of the Doctor (2013).
An Unearthly Child (1963), the first episode of Doctor Who, revealed that the Doctor and Susan were “exiles… cut off from our own planet,” with Susan confirming, “I was born in another time, another world.” So the old man and his granddaughter weren’t just travellers from Earth’s future, but unequivocally alien. In subsequent episodes there were teasing references to the Doctor’s home world: in The Sensorites (1964), for example, Susan describes it as being “quite like Earth, but at night the sky is a burnt orange, and the leaves on the trees are bright silver.”
A publicity shot of Carole Ann Ford as Susan and William Hartnell as the Doctor from the series’ first episode, An Unearthly Child (1963).