17 April 1924: birth of Clyde Pollitt, who played a Time Lord (the Chancellor) in The War Games (Second Doctor, 1969) and The Three Doctors (Third Doctor, 1973)
also 17 April 1924: birth of Kevin Lindsay, who played Linx in The Time Warrior (1973-74), Cho Je in Planet of the Spiders (1974), and Styre/The Marshal in The Sontaran Experiment (1975).
17 April 1941: birth of Brian Miller, who played Dugdale in Snakedance (1983), Harry Sowersby in The Mad Woman in the Attic (SJA, 2009) and Barney the tramp in Deep Breath (Twelfth Doctor, 2014); Elisabeth Sladen was his wife.
17 April 1942: birth of David Bradley, who played William Hartnell playing the First Doctor in An Adventure in Space and Time (2013) and then played the First Doctor in The Doctor Falls and Twice Upon A Time (both Twelfth Doctor, 2017).
ii) broadcast anniversaries
17 April 1965: broadcast of "The Warlords", fourth episode of the story we now call The Crusade. Barbara escapes; Ian retrieves her, the Doctor and Vicki; and the time travellers depart.
17 April 1971: broadcast of second episode of Colony in Space. Jo talks to the colonists, and the Doctor talks to the IMC; and is threatened by the killer robot, again.
17 April 2010: broadcast of Victory of the Daleks. Receiving a call for help from his old friend Winston Churchill, the Doctor and Amy head for World War II. But why are the Daleks passing themselves off as man-made weapons? And why don't they recognise the Doctor?