23 May 1964: broadcast of "Temple of Evil", first episode of the story we now call The Aztecs. The Tardis lands in medieval Mexico, where Barbara is received as the reincarnation of the priest Yetaxa.
23 May 1970: broadcast of third episode of Inferno. The Doctor realises that he has travelled to a parallel Earth. (This is the one with the famous eyepatch scene.)
23 May 1988: release of "Doctorin' the Tardis" by The Timelords (later the KLF). A true cultural
23 May 2003: webcast of fourth episode of Shada. The Doctor and Chris discover Skagra's store of genius minds.
23 May 2020: broadcast of Doctors Assemble! All of the Doctors, though none played by the original actors.