Last of the Time Lords
In the episode "Last of the Time Lords", the immortal time traveller Captain Jack Harkness expresses concern about how he might look if he lives "for a million years", because although he cannot die, he is still aging, albeit slowly. He tells the Doctor and Martha Jones that it is a matter of vanity, because as the first person from the Boeshane Peninsula to join the Time Agency, he was featured on posters, becoming known as "the Face of Boe".