8 October 1966
Robert Beatty (General Cutler), Dudley Jones (Dyson), David Dodimead (Barclay), Alan White (Schultz) [1-2], Earl Cameron (Williams) [1-2], Shane Sheldon (Tito) , John Brandon (American Sergeant) , Steve Plytas (Wigner), Christopher Matthews (Radar Technician), Reg Whitehead (Krail) , Harry Brooks (Talon) , Gregg Palmer (Shav) , Ellen Culler (Geneva Technician) [3-4], Glenn Beck (TV Announcer) , Roy Skelton [2,4], Peter Hawkins  (Cybermen Voices), Christopher Dunham (R/T Technician) [3-4], Callen Angello (Terry Cutler) [3-4], Harry Brooks (Krang) , Reg Whitehead (Jarl) , Gregg Palmer (Gern) .
|Written by||Kit Pedler/Gerry Davis|
|Directed by||Derek Martinus|
|Produced by||Innes Lloyd|
The TARDIS lands near an international tracking station in Antarctica. The year is 1986, and the Doctor, Polly and Ben are just in time to witness the arrival in the solar system of Mondas, a planet which is the mirror image of Earth. Soon, Mondas’ natives, the Cybermen — humans who have replaced much of their living tissue with cybernetic attachments — invade the tracking station, as Mondas begins to drain the Earth of its energy. The time travellers must stop the process before the Cybermen begin to convert all humanity into creatures like themselves… but something is very wrong with the Doctor.
- First appearance of the Cybermen
- This is the first regeneration (though the term is never used until 1974 in Planet of the Spiders), from William Hartnell’s Doctor into Patrick Troughton‘s Doctor.
- Episode 4 is missing from the BBC archives. Only several short clips of footage exist, among which are the regeneration sequence itself, the sequence exists through being used on a contemporary entertainment news programme to discuss the transition to the new Doctor.
- William Hartnell left Doctor Whodue to bad health, but upon leaving had said “If there is one man in England, who can replace me as the Doctor, it’s Patrick Troughton!” Troughton took over the role of the Doctor when Hartnell regenerated into Troughton. Hartnell returned in The Three Doctors in 1973 to celebrate the show’s 10th anniversary, but died two years later.
- The Doctor does not appear in Episode 3, as William Hartnell was unwell during the week when it was recorded.
- Special “computer tape”-style opening and closing title graphics were created for this story by graphic designer Bernard Lodge.
- This is the only story to give Cybermen characters individual names (Krang, Jarl, etc). After this, Cybermen were only ever named by rank (Cyberleader, Cybercontroller, etc).
- At the time of the serial’s original broadcast, as well as the timeframe of the serial (1986),Plutowas still considered a planet and therefore the story title and dialogue referring to Mondas as the solar system’s tenth planet was correct. In 2006, Pluto lost its planetary status, which would make Mondas officially the ninth planet, not the tenth.Note: By the newly-adopted criteria which excludes Pluto, Mondas would technically not be considered a planet either.
- In Episode 4, the Doctor is credited as “Doctor Who” instead of the usual “Dr. Who”.