i) births and deaths

15 December 1926: death of Chritopher Burgess, who played the underground exile leader Swann in The Enemy of the World (Second Doctor, 1968), radio astronomer George Philips in Spearhead from Space (Third Doctor, 1970) and chief meditator Barnes in Planet of the Spiders (Third Doctor, 1974)

15 December 1940: birth of Pennant Roberts, who directed The Face of Evil (Fourth Doctor, 1977), The Sun Makers (Fourth Doctor, 1977), The Pirate Planet (Fourth Doctor, 1978), Shada (Fourth Doctor, unbroadcast but would have been 1980), Warriors of the Deep (Fifth Doctor, 1984) and Timelash (Fifth Doctor, 1985).

15 December 1945: birth of Sarah Hellings, who directed Mark of the Rani (Sixth Doctor, 1985).

15 December 1985: birth of John Magnus Jones, who directed several stories of New Who Series 12 (Thirteenth Doctor, 2020)

15 December 1998: death of Peter Mayock who played Ibrahim Namin in Pyramids of Mars (Fourth Doctor, 1975) and Solis in The Deadly Assassin (Fourth Doctor, 1976).

ii) broadcast anniversaries

15 December 1973: broadcast of first episode of The Time Warrior, starting Season 11. First appearance of both Elizabeth Sladen as Sarah Jane Smith and the Sontarans. Scientists are being kidnapped through time to the medieval castle of Irongron, where his mysterious guest Linx is forcing them to repair his spaceship.

15 December 1979: broadcast of fourth episode of Nightmare of Eden. The ships are separated and the Doctor captures the bad guys in the projection.