11 April 1940: birth of Sheila Dunn, who played Blossom Lefavre in The Daleks' Master Plan (First Doctor, 1965), the computer voice of the Electromatic company in The Invasion (Second Doctor, 1968), and Petra Williams in Inferno (Third Doctor, 1970). She was married to Douglas Camfield, who directed all three of those stories.
11 April 2005: death of John Bennett, who played General Finch in Invasion of the Dinosaurs (1974) and (shamefully in yellowface) Li H'sen Chang in The Talons of Weng-Chiang (1977).
11 April 2010: death of Richard Shaw, who played Governor Lobos in The Space Museum (First Doctor, 1965), treacherous prisoner Cross in Frontier in Space (Third Doctor, 1973) and also Lakh, one of the imperviously helmeted Seers in Underworld (Fourth Doctor, 1978).
ii) broadcast anniversaries
11 April 1964: broadcast of "The Sea of Death", first episode of the story we now call The Keys of Marinus. Arbitan, Keeper of the Conscience of Marinus, sends the Tardis crew to find the lost keys of the machine.
11 April 1970: broadcast of fourth episode of The Ambassadors of Death. The aliens go on the rampage at the Space Centre.
11 April 2009: broadcast of Planet of the Dead. A London bus is transported to a desert planet via a wormhole, its passengers including the Doctor and high-class thief Christina de Souza.
11 April 2020: release of Rory's Story.