4th August 1941: birth of Martin Jarvis who played Hilio in The Web Planet (1963), Butler in Invasion of the Dinosaurs (1974), and the Governor in Vengeance on Varos (1985).
4th August 1971: birth of Fenella Woolgar who played Agatha Christie in The Unicorn and the Wasp (2008).
4th August 1989: death of Maurice Colbourne who played Lytton in Resurrection of the Daleks (1984) and Attack of the Cybermen (1985).
ii) broadcast anniversary
4th August 2016: Peter Capaldi is announced as the Twelfth Doctor.
iii) date specified in-universe
From Paul Cornell's (excellent) 1992 Seventh Doctor novel Love and War, which introduced Bernice "Benny" Summerfield:
Benny pulled a thick volume from the stuffed bookshelf behind the Doctor. Resting it on her lap, she found a place with her finger and began to read. 'August the fourth. This is my diary, by the way . . .'
'Is this relevant?'
'Oh yes, very. This is from a year when I had a tremendous crush on a young research assistant. "Dear Diary, I hate myself. And I'm afraid that means I hate you too. Those who read this will just have to get used to a deterioration in our relationship" '
The Doctor was smiling. 'Do you often stage readings?'
'Yes, and I annotate all over the place, and sometimes I go back and stick notes over the bits I don't like. I don't want to erase them, so you can peel off the note, but I want to offer a . . . a new version, I suppose. This is one of those pieces. Here's where we get on to the note. This is the new version.' Benny peeled off a scrap of pink paper and read it out. 'I took Ian out dancing, to the Elderstrasse Ballroom, and it was great. He told me that I was like a sister to him, which was very flattering.' She sighed, and crumpled the note up. 'History is written by the winning side. That's why nobody in this century has ever heard of Exeter City.'
'Ah . . . ' The Doctor looked puzzled once more.
'This, however, is what really happened. I took Ian dancing, had a few too many glasses of wine, told him that I loved him and got real y hurt when he told me he thought of me as a sister. I ran out down the steps and ruined a perfectly good dress in the fall. A Styhian beggar helped me out of the gutter. I told him that we were both looking at the stars, and gave him most of my cash.' Benny thumped the book closed. 'So what do you think?'
'The real version's better.'