i) births and deaths

11 September 1921: birth of Edwin Richfield, who played Captain John Hart in The Sea Devils (Third Doctor, 1972) – not the Captain John Hart of later Torchwood! – and also Mestor in The Twin Dilemma (Sixth Doctor, 1984). I think it's reasonably clear which part required more make-up…

11 September 1981: birth of Lachlan Niebohr, who played Jack's brother Gray in the second season of Torchwood (2008). (So what happened to him after the Hub was blown up?)

11 September 1987: death of Hugh David, who directed The Highlanders (Second Doctor, 1966-67) and Fury from the Deep (Second Doctor, 1968). As an actor, he was one of those approached about playing the role of the Doctor back in 1963, but turned it down.

ii) broadcast anniversaries

11 September 1965: broadcast of "Four Hundred Dawns", first episode of the story we now call Galaxy 4, starting Season 3 of Old Who. The Doctor, Steven and Vicki land on a remote planet where the Drahvins and Rills (the latter assisted by the robot Chumblies) are at odds. But the Doctor discovers that the planet will explode the day after next.

11 September 1976: broadcast of episode 2 of The Masque of Mandragora. The Doctor escapes execution, and Sarah escapes sacrifice, but is recaptured by the cultists.

11 September 2015: release of the Prologue to Season 9 of New Who – I admit I hadn't seen this before until I wrote today's entry.

iii) date specified in-universe

11 September 1960: birth of Clara Oswald's mother Ellie (née Ravenswood).