The first story to mention how many regenerations a Time Lord has was the Fourth Doctor story ‘The Deadly Assassin’ in 1976.
Philip Madoc appeared in ‘The Krotons’, ‘The War Games’, ‘The Brain of Morbius’ and ‘The Power of Kroll’ in the classic era of Doctor Who, but was first involved with the programme when he appeared in the film ‘Dalek – Invasion 2150 AD’, which starred Peter Cushing as the Doctor. 
The evil Salamander looked identical to the Second Doctor in ‘The Enemy of the World’, which saw Patrick Troughton taking on both roles. ‘The Android Invasion’ showed the Kraals create a fake Earth, and ‘The Androids of Tara’ had Mary Tamm playing Romana, Princess Strella, and their two android doubles.
The first script by Douglas Adams to appear in Doctor Who was ‘The Pirate Planet’ in Season 16. Adams wrote under the pseudonym of David Agnew for the Season 17 story ‘City of Death’, and became world-famous during this time for ‘The Hitchhiker’s Guide to the Galaxy’.
The two stories to feature Sil in the classic era of Doctor Who were called ‘Vengeance on Varos’ and ‘Mindwarp’, and starred Nabil Shaban. It was planned for Sil to appear alongside the Ice Warriors in ‘Mission to Magnus’, which was eventually abandoned when the series was put on hiatus.
The first story to introduce the Cybermen in the classic era of Doctor Who was ‘The Tenth Planet’, and the last in the classic era was ‘Silver Nemesis’. The Patrick Troughton story ‘The Tomb of the Cybermen’ was the first to feature the Cybermats, and David Banks played the Cyber-Leader between ‘Earthshock’ and ‘Silver Nemesis’.
The original makeup design for the Vinvocci was not completely green, with their faces natural. After filming had finished, Russell T Davies reconsidered the creatures’ design and decided to have the footage digitally recoloured at a very expensive cost.
The Doctor’s Christmas companions of the revived era have been Rose Tyler, Donna Noble, Astrid Peth, Jackson Lake, and Wilfred Mott. The two guest actors who will appear in ‘A Christmas Carol’ are Michael Gambon and Katherine Jenkins, and they will play the roles of Kazran Sardick and Abigail Pettigrew.
The red spiky alien who appeared in ‘Voyage of the Damned’ was called Bannakaffalatta and came from the Zocci race, and the green spiky aliens who appeared in ‘The End of Time’ were called Rossiter and Addams, and came from the taller Vinvocci race.
The first ever episode of Doctor Who to be broadcast on Christmas Day was ‘The Feast of Steven’, which was the seventh part of ‘The Daleks’ Master Plan’. At the end of the episode the Doctor turns to the camera and says: “Oh and incidentally, a happy Christmas to all of you at home.”
The original Doctor Who theme tune was composed by Ron Grainer and arranged by Delia Derbyshire at the BBC Radiophonic Workshop. There have been eight distinct variants of the theme tune on television (4 in the classic era, 1 in the TV Movie, 3 in the revived era).
The four most common recurring monsters of the sixties in Doctor Who were the Daleks who first appeared in ‘The Daleks’, the Cybermen who first appeared in ‘The Tenth Planet’, the Ice Warriors who first appeared in ‘The Ice Warriors’, and the Yeti who first appeared in ‘The Abominable Snowmen’.
The first Doctor Who story to be shown as part of Children in Need was the twentieth anniversary story ‘The Five Doctors’, and the charity story which saw a crossover with Eastenders was ‘Dimensions in Time’.
The Krynoid monster was created from the same costume as the Axon monster, and was sprayed green. It appeared in the Tom Baker story ‘The Seeds of Doom’.
The sonic devices to appear in Doctor Who include the sonic screwdriver, sonic blaster, sonic lipstick and sonic lance, and the laser devices include the laser screwdriver and a mention of the laser spanner.
The Sontarans made a famous appearance on ‘Jim’ll Fix It’ in the eighties, and last appeared on Doctor Who in ‘The Pandorica Opens’ and ‘The End of Time – Part 2’.
The different ranks of Cybermen that have appeared in the show ever since their first story are the Cyber Controller, Cyber Mat, Cyber Leader, Cyber Lieutenant, Stealth Cyberman, Cyber Shade and Cyber King.
The actors who have appeared in both episodes of Doctor Who and the film Hot Fuzz are Simon Pegg (The Editor in The Long Game), Anne Reid (Plasmavore in Smith and Jones) Timothy Dalton (Rassilon in The End of Time), Olivia Colman (Human Form Prisoner Zero in The Eleventh Hour), and Bill Nighy (Dr. Black in Vincent and the Doctor).
Graeme Harper has directed for the Fourth, Fifth, Sixth and Tenth Doctors on Doctor Who, and was a partial Director for ‘Warriors’ Gate’, and a full Director for ‘The Caves of Androzani’ and ‘Revelation of the Daleks’ in the classic era of the show.
The last scene of Doctor Who to be shown in black and white was Patrick Troughton’s regeneration in ‘The War Games’, and the first scene to be shown in colour was the tracking of the meteorites in ‘Spearhead from Space’.