The original script was written by Terrance Dicks, using some ideas from his script of the stage play
Doctor Who and the Daleks in the Seven Keys to Doomsday to a requirement from Hinchcliffe for a story about a human/robot relationship. However, after delivery Dicks was out of the country when it was decided that the robot, core to the story, could not be realised under the budget constraints. In excising the character,
script editor Robert Holmes had to undertake the substantial rewrites without informing Dicks, who could not be contacted. The robot character was replaced with Solon who required a different motivation—that of a mad scientist. Dicks later said of the decision that it was not original but it was the "only one available". Upon his return to the United Kingdom, Dicks learnt of the changes and angrily phoned Holmes. Since the work was more Holmes than his own, Dicks demanded the removal of his name from the credits saying it could go out under a "bland
pseudonym". The episodes were recorded entirely in studios during October 1975.
Cast notes Philip Madoc had already appeared in
The Krotons (1968–69) and
The War Games (1969) and would appear afterwards in
The Power of Kroll (1978–79). He also had a role in the film ''
Daleks' Invasion Earth 2150 A.D. (1966) and appeared in the audio plays Master and Return of the Krotons''. Colin Fay was a fortunate find for the production team: an opera singer by trade, he was a large man and, as a newcomer to television, cheap to hire. Other cost cutting included hiring only a single professional dancer who was copied in the scenes by actresses who had been chosen because of previous dancing experience.
Faces in the mind-bending sequence During the Doctor's mental battle with Morbius, the mind-bending machine displays two images of Morbius, then images of the Doctor's four incarnations as of the serial's production. These are followed by images of eight previously unseen faces, intended to represent incarnations preceding the
First Doctor. The Doctor's previous faces are almost all portrayed by members of the
Doctor Who crew who worked on this serial or the following serial,
The Seeds of Doom: production unit manager
George Gallaccio, script editor
Robert Holmes, production assistant
Graeme Harper, director
Douglas Camfield, producer
Philip Hinchcliffe, production assistant (who is the exception as he has no credits on
Doctor Who), writer
Robert Banks Stewart, and director
Christopher Barry. Hinchcliffe stated, "We tried to get famous actors for the faces of the Doctor. But because no one would volunteer, we had to use backroom boys. And it is true to say that I attempted to imply that
William Hartnell was not the first Doctor". After a complaint that actors were not used, the BBC paid a sum of money to the acting union
Equity's benevolent fund. In 2020 it was announced that Hinchcliffe, Gallaccio and Harper had all returned to reprise their roles as the Doctor for an unofficial
fan film entitled
The Timeless Doctors produced by multimedia artist
Stuart Humphryes. The
season 14 story
The Deadly Assassin introduced the idea that Time Lords are limited to 12 regenerations. The
season 10 story
The Three Doctors, produced and aired before both
The Brain of Morbius and
The Deadly Assassin, calls the William Hartnell Doctor the "earliest Doctor". Attempts to retrofit this with the number of faces seen in the mind test machine have brought about explanations including the possibility that the faces were Morbius' previous incarnations, younger versions of the First Doctor, or the Doctor's potential future incarnations. The
Virgin Missing Adventure Cold Fusion by
Lance Parkin implies that one of these prior Doctors was the incarnation of the Doctor active at the time of the birth of
Susan Foreman. However, the subsequent
Virgin New Adventures novel
Lungbarrow states that Hartnell's Doctor was the first, implying instead that the faces represent incarnations of
the Other, one of the founders of
Time Lord civilisation, of whom
the Doctor is the reincarnation. The
series 12 episode "
The Timeless Children" (2020) confirmed that the faces were indeed incarnations pre-dating the First Doctor; the same story also confirmed that the Doctor was not previously subject to the same regeneration limit as the rest of the Time Lords. ==Broadcast and reception==