i) births and deaths
21 October 2000: death 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).
21 October 2007: death of Peter Moffatt, who directed State of Decay (Fourth Doctor, 1980), The Visitation (Fifth Doctor, 1982), Mawdryn Undead (Fifth Doctor, 1983), The Five Doctors (Fifth Doctor era, 1983), The Twin Dilemma (Sixth Doctor, 1984) and The Two Doctors (Sixth Doctor era, 1985).
21 October 2009: death of Chris D'Oyly-John who worked in various production capacities on fifteen Classic Who stories from The Ark (First Doctor, 1966) to The Talons of Weng-Chiang (Fourth Doctor, 1977).
ii) broadcast anniversaries
21 October 1967: broadcast of fourth episode of The Abominable Snowmen. Victoria is hypnotised by Padmasambhava; the monks evacuate; and the Intelligence grows in physical manifestation.
21 October 1978: broadcast of fourth episode of The Pirate Planet. Xanxia killes the Captain; the Mentiads destroy her and the bridge; and the Doctor and Romana convert the remains of the planet Calufrax into the second segment of the Key to Time.
21 October 2019: broadcast of Rosa. The Doctor and team find themselves in civil-rights era Alabama.