21 June 1991: death of Ivor Salter, who played the Morok Commander in The Space Museum (1965), Odysseus in The Myth Makers (1965), and Sgt. Markham in Black Orchid (1982).
ii) broadcast anniversaries
21 June 1969: broadcast of tenth episode of The War Games, ending Season 6 of Old Who. Last regular appearance of Patrick Troughton as the Second Doctor, Frazer Hines as Jamie and Wendy Padbury as Zoe.
21 June 2008: broadcast of Turn Left. Donna is thrust into an alternate universe where the Doctor was killed during the events of The Runaway Bride, and the situation continues to deteriorate until she sacrifices herself to change her previous self's destiny.
iii) dates specified in canon
21 June was usually when Torchwood defrosted Tommy Brockless (as mentioned in To The Last Man in 2008).
21 June 2540: birth of Bernice Summerfield (at least according to the 1999 Big Finish audio Just War).