21 May 1966: broadcast of "The O.K. Corral", last episode of the story we now call The Gunfighters, and the last episode before 2005 to have an individual title. Doc Holliday and the Earps shoot it out with the Clantons, to the detriment of the latter.
21 May 2005: broadcast of The Empty Child; first appearance of Captain Jack Harkness and first contribution to New Who by Steven Moffat. The Doctor and Rose find London in the Second World War infested by zombies with gas-masks.