21 November 1924: birth of Malcolm Hulke, co-author of The Faceless Ones, The War Games and (uncredited) The Ambassadors of Death, sole author of Doctor Who and the Silurians, Colony in Space, The Sea Devils, Frontier in Space, and Invasion of the Dinosaurs, and writer of seven novelisations (DW&t Cave-Monsters, DW&t Doomsday Weapon, DW&t Sea Devils, DW&t Green Death, DW&t Dinosaur Invasion, DW&t Space War and DW&t War Games) and co-writer of The Making of Doctor Who. See in particular this long and fascinating blog post: Doctor Who and the Communist: the work and politics of Malcolm Hulke (1924-1979), by Michael Herbert
21 November 1937: birth of Ingrid Pitt, who played Galleia in The Time Monster (Third Doctor, 1972) and Solow in Warriors of the Deep (Fifth Doctor, 1984) and co-wrote The Macros (originally submitted in the mid-80s, made by Big Finish as a Sixth Doctor story in 2010).
21 November 2015: death of Anthony Read, script editor in 1978/79 for the final Leela stories and the complete Key to Time season, author of The Horns of Nimon (Fourth Doctor, 1979-80) and co-author of The Invasion of Time (Fourth Doctor, 1978).
ii) broadcast and webcast anniversaries
21 November 1964: broadcast of "World's End", first episode of the story we now call The Dalek Invasion of Earth. The Tardis lands in a future devastated London; Susan and Barbara fall in with the human resistance, and the Doctor and Ian are captured by the Daleks.
21 November 1990: broadcast of Search Out Space, an episode of the BBC show Search Out Science featuring Sylvester McCoy as the Seventh Doctor, Sophie Aldred as Ace and John Leeson as the voice of K9. Haven't seen it and it's not in most people's concept of canon.
21 November 2009: release of first episode of Dreamland, animated story starring David Tennant as the Doctor, Georgia Moffatt as Cassie Rice and Tim Howar as Jimmy Stalkingwolf. The Doctor lands at a diner in Nevada, where a mysterious artifact attracts the Men in Black...
21 November 2015: broadcast of Face the Raven. Clara takes on the burden of the death tattoo - with consequences.
iii) date specified in canon
21 November 2059: setting for most of the events of The Waters of Mars (2009).