4 January 1964: broadcast of "The Escape", third episode of the story we now call The Daleks. Susan meets Alydon the Thal in the forest, and returns to the others in the city, where they capture a Dalek.
4 January 1969: broadcast of second episode of The Krotons. Zoe and the Doctor take the test and enter the machine; the Krotons manifest themselves.
4 January 1975: broadcast of second episode of Robot. K1, the robot, kills a cabinet minister and threatens to kill the Doctor.
4 January 1982: broadcast of first episode of Castrovalva first full story with Peter Davison as the Fifth Doctor, starting Season 19 of Old Who. The new Doctor collapses; Adric is captured by the Master; and the Tardis is heading back to the Big Bang...
4 January 1989: broadcast of fourth episode of The Greatest Show in the Galaxy, ending Season 25. The Gods of Ragnarok are behind the circus; the Doctor defies them and the circus collapses into rubble.