23 September

History of the Doctor Who Universe
1215 - Birth of Kublai Khan, who will meet the Doctor and companions in Marco Polo.

History of Doctor Who
1967 - The Tomb of the Cybermen Episode 4 First Broadcast

1978 - The Ribos Operation Episode 4 First Broadcast

2006 - Patrick Tull, one of the voices of the Krotons in The Krotons dies