2. The Weeping Angels aren't props – they're played by actresses in stone costumes who have to stay very, very still.
3. The noise the TARDIS makes was created by rubbing piano strings with a key.
4. Nicholas Briggs, the voice of the Daleks in recent series, had to bring along his own analogue voice modulator to create the voice as the BBC couldn't find a way to replicate their distinctive sound digitally.
5. In an early draft of the very first Doctor Who script, it's strongly implied that the Doctor is planning to kill future companions Ian and Barbara in order to protect his secret. This was quickly taken out.
6. Wendy Padbury, the agent who discovered Matt Smith as a young actor, played the second Doctor's companion Zoe Heriot in the late 1960s.
7. In fact, three of the actresses who played the Doctor's companions went on to become agents, and all of them ended up representing actors who would play the Doctor.
8. In 1988, Paramount Pictures wanted to make a Doctor Who movie starring either Michael Jackson or Bill Cosby as the Doctor.
9. The first Doctor Who novel had the unwieldy title Doctor Who in an Exciting Adventure With the Daleks.
10. The name "Time Lord" to describe the Doctor's people wasn't used until 1969, five-and-a-half years after the show started. It was another four-and-a-half years before his home planet was named on screen as "Gallifrey".
11. Shouty actor Brian Blessed claims he was offered the role of the Second Doctor (which eventually went to Patrick Troughton), but turned it down.
12. Other than the TARDIS herself, the companion that was with the Doctor for the longest time was probably Handles the disembodied Cyberman head.
13. Peter Capaldi used to be in a punk band with Late Late Show host Craig Ferguson:
14. The Doctor has been married three times (that we know about) – to Queen Elizabeth I, Marilyn Monroe, and River Song.
15. Tennant is married to Georgia Moffett, who played the Doctor's daughter opposite him in "The Doctor's Daughter" and is actually the daughter of the fifth Doctor, Peter Davison. So the couple's children have Doctors for their father and grandfather.
16. Tom Baker's famously long scarf as the fourth Doctor was created partly by accident. The knitter hired to create it, Begonia Pope, wasn't told how long it needed to be, so just used up all the wool she was given. It ended up 20 feet long (but was eventually trimmed down a bit).
17. In 2009 a group of volunteers clearing a pond in Hampshire found a submerged Dalek. It's not clear how it got there.
18. The gas masks in "The Empty Child" were made in part from cans of baked beans after attempts to find authentic WWII gas masks failed because they contain dangerous asbestos.
19. Peter Capaldi and sixth Doctor Colin Baker are the only actors to have been cast as the Doctor after previously appearing in the series as another character.
20. The 2008 episode "The Fires of Pompeii" was notable for having a future companion and a future Doctor in its cast as different characters – Karen Gillan and Capaldi.
21. Peter Hawkins, the original voice of the Daleks, went on to voice the character of Zippy in children's TV show Rainbow. He was replaced as Zippy after the first series by Roy Skelton – who had also replaced him as the voice of the Daleks.
22. As teenagers, fourth Doctor Tom Baker trained to become a Roman Catholic monk, and seventh Doctor Sylvester McCoy trained to become a priest.
23. A 1966 internal BBC memo about the Doctor's first regeneration suggested it was supposed to be like a really bad LSD trip:
24. One of the earliest story ideas for Doctor Who was a version of Dickens' A Christmas Carol, but with a "slightly tipsy" Doctor as Jacob Marley. (The series finally did a loose adaptation of A Christmas Carol in 2010, but with added sharks.)
25. Verity Lambert, Doctor Who's first producer, was both the youngest producer in the BBC's drama department and the only woman in such a role.
26. In a previous job on ITV's Armchair Theatre series in 1958, Lambert – then just a production assistant – had to unexpectedly step in to studio-direct a live broadcast of a play after one of the actors died during transmission.
27. A teenage Capaldi had his Doctor Who fan art published in Doctor Who International Fan Club Magazine.
28. The young Capaldi was so desperate to be put in charge of the Official Doctor Who Fan Club that he bombarded the BBC with letters to the point where the producer's secretary said: "I wish the Daleks or someone would exterminate him."
29. In 2007, Hugh Grant told The Sun that he'd been offered the role of the Doctor but turned it down because he didn't think the new show would be a success.
30. The person who was originally supposed to design the Daleks was Ridley Scott – later the director of Alien and Gladiator – but he left his job at the BBC before he could get around to it.
31. An audience research report from 1988 showed that Bonnie Langford's character, Mel, was "unpopular" (to say the least) with viewers – "56% of respondents who answered a questionnaire on the Paradise Towers story wished she had been eaten".
32. The 1965 episode "Mission to the Unknown" is the only one in the series' history that doesn't feature the Doctor, the TARDIS, or any of his companions.
33. Alternative costume designs for Smith included one design that was described as being like a pirate:
34. The Daleks might never have existed if comedian Tony Hancock hadn't had a massive row with his then scriptwriter, Terry Nation. Nation was about to decline an offer to write the second Doctor Who story, but changed his mind when Hancock sacked him that night – luckily, before his agent had had a chance to turn the BBC down.
35. Doctor Who's main creator, Sydney Newman, was furious about the inclusion of the Daleks, as he'd been adamant that he didn't want clichéd "bug-eyed monsters" in his show. (He later admitted he might have been wrong about this.)
36. The fourth Doctor advertised computers on televison.
37. The words "Dalek" and "TARDIS" have become so widely used that they now both appear in the Oxford English Dictionary.
38. It's not entirely clear what the Doctor is a doctor of. Over the years, he's both claimed that he is a medical doctor and also denied it.
39. In 1995, Steven Moffat posted a "particularly stupid" fan theory to a Doctor Who news group. Sixteen years later, he used it as part of the plot of "A Good Man Goes to War".