1. Courtney was born in Cairo, Egypt, the son of a British diplomat, and was educated in France, Kenya and Egypt. On his maternal side, Courtney was descended from the New Zealand politician John Cuff.
2. He did his national service in the British Army, leaving after 18 months as a private, not wanting to pursue a military career.
3. He made guest appearances in several cult television series, including The Avengers , hosting a debate between John Bird and John Fortune.
4. Director Douglas Camfield originally considered Courtney for the role of Richard the Lionheart in the Doctor Who serial “The Crusade” , a role that ultimately went to Julian Glover.
5. Camfield made sure to keep Courtney in mind for future casting, however.
6. However, when David Langton gave up the role of Colonel Lethbridge-Stewart to work elsewhere, Camfield recast Captain Knight and gave the part to Courtney instead. and in charge of British contingent of UNIT.
7. The organisation had been charged with protecting the Earth from alien invasion.
8. Years later Ian Marter, who played UNIT medical officer Harry Sullivan alongside Tom Baker, named a Russian military base used in “The Invasion”, but unnamed on screen, “Nykortny” in his novelisation of the story.
9. It was in this recurring role that he would become best known to the viewing audience, appearing semi-regularly in 101 episodes between 1970 to 1975.
10. The character proved popular enough to return in 1983, first in “Mawdryn Undead” and in the official 20th anniversary special The Five Doctors.
11. Marsh also appeared in the earlier story “The Crusade” for which Courtney had been considered.
12. Courtney has played Lethbridge-Stewart, either on television or in spin-off audio plays, alongside every subsequent Doctor up to and including Paul McGann, as well as substitute First Doctor Richard Hurndall.
13. He did not act in the revived series, although he did so in the spin-off, The Sarah Jane Adventures and appeared in archival footage in Doctor Who proper.
14. While he has acted with Tenth Doctor actor David Tennant in the Big Finish audio dramas Sympathy for the Devil and UNIT: The Wasting, Tennant was playing a different character, Colonel Ross Brimmicombe-Wood, on both occasions.