8 January 1908: they don't get more fundamental than this: birth of William Hartnell, who played the First Doctor from 1963 to 1966, and returned for The Three Doctors in 1972-73.
ii) broadcast anniversaries
8 January 1966: broadcast of "Golden Death", the ninth episode of the story we now call The Daleks' Master Plan. Both the Doctor's Tardis and the Monk's arrive in ancient Egypt, pursued by the Daleks and Mavic Chen.
8 January 1971: broadcast of second episode of Day of the Daleks. Jo is captured and brought to the 22nd Century; the Doctor is confronted by a Dalek emerging from the time vortex.
8 January 1977: broadcast of second episode of The Face of Evil. The Doctor passes the Test of the Horda; Xoanon unleashes the invisible monsters on the Sevateem.