14 December 1926: birth of Margaret John, who played Megan Jones, the Director of Euro Sea Gas, in Fury from the Deep (Second Doctor, 1968) and The Idiot's Lantern (Tenth Doctor, 2006), a 38-year gap which is unmatched for the main TV show (spinoffs allow some flexibility)
14 December 1926: birth of Alan Rowe, who played Evans and the voice of Space Control in The Moonbase (Second Doctor, 1967), Edward of Wessex in The Time Warrior (Thrd Doctor, 1973-74), Skinsale in Horror of Fang Rock (Fourth Doctor, 1977) and Garif in Full Circle (Fourth Doctor, 1980).
14 December 1933: birth of David Maloney, who was one of the great directors of the classic series: The Mind Robber (1968), The Krotons (1968-69), The War Games (1969), Frontier in Space (1963), Planet of the Daleks (1963), Genesis of the Daleks (1975), Planet of Evil (1975), The Deadly Assassin (1976), and The Talons of Weng-Chiang (1977) all benefited from his talents.
14 December 2018: death of Kenneth Kendall, who appeared as a newsreader in The War Machines (1966), the first celebrity to portray himself on Doctor Who (unless you count the Beatles). He's also in 2001: A Space Odyssey in a similar role.
ii) broadcast anniversaries
14 December 1963: broadcast of "The Firemaker", fourth episode of the story we now call An Unearthly Child. Ian makes fire for Za, who defeats Kal and tries to force the time travellers to stay with the tribe; but they escape.
14 December 1978: broadcast of seventh episode of The Invasion. UNIT successfully uses a Russian rocket to destroy the source of the Cybermen's signal.
14 December 1988: broadcast of first episode of The Greatest Show in the Galaxy. The Doctor and Ace land on Segonax and are captured by the Psychic Circus.