William Hartnell, who played the Doctor in the television series, was reportedly very disappointed to be replaced by Peter Cushing for the film. Cushing was cast because he was better known to US audiences.
As an incentive Roberta Tovey (who was 11 at the time the film was produced) was paid a shilling (5p) by director Gordon Flemyng every time she did a scene in one take. She made so much money, Flemyng didn't offer her the same deal for the sequel.
Other notable changes between the TV series and the film version: in the film, Dr. Who has two grandchildren - Susan and Barbara (in the TV series only Susan is related to the Doctor). Ian is Barbara's boyfriend (in the TV series they were teachers, working at the same school). The Daleks used for this film and its sequel were slightly re-designed for the big screen. The BBC acquired a number of these Daleks after principle photography was complete - and movie-style Daleks in fact appeared on TV (in 1965's "The Chase") before the movie was even released.
A number of changes were made to the main characters in the process of transferring "Doctor Who" to the big screen. Most importantly, The Doctor is shown to be a human scientist named Dr. Who. In the TV series, the lead character is an alien time-traveler, specifically a Time Lord from the planet Gallifrey (although this back story had not been invented when this film was made) and whose name is never revealed, and who is referred to as "The Doctor" or, less frequently, "Doctor Who".
Gordon Flemyng did not originally realise that the Daleks' dome lights only flash in synchronisation with their speech, and consequently had them randomly pulse to make their scenes more visually interesting. This caused problems for Milton Subotsky when the film was assembled in post-production: editing the footage meant that he had to severely rewrite some dialogue to fit the flashes. This resulted in unavoidably staccato delivery for the creatures.
It was planned to show one of the denizens of the swamp of mutations, but the prop constructed for the sequence was deemed rather unconvincing. In contrast, a writhing creature designed to be glimpsed inside a Dalek casing was judged too unsettling for the family audience the film was aimed at.
The screenplay to this film was credited to producer Milton Subotsky, with additional material by David Whitaker. In fact, Dalek creator Terry Nation only agreed to license his teleplay to Subotsky if Whitaker (who was Nation's script editor when he wrote the original teleplay) was hired to adapt it. A deal was therefore struck that would allow Subotsky to receive the credit despite the screenplay actually being written by Whitaker.
The edition of "The Eagle and Boys' World" read by Dr. Who is Volume 16, Number 12, published Saturday 20th March 1965. Susan reads Eric M. Rogers' 1960 textbook "Physics for the Inquiring Mind; The Methods, Nature, and Philosophy of Physical Science", whilst Barbara peruses "The Science of Science".
Actress Yvonne Antrobus was unavailable for post-synchronization after the shooting of the film was complete. Thus, while she is seen on-screen as Dyoni, her voice is provided by another, unnamed, actress.
Peter Hawkins and David Graham provide the uncredited Dalek voices in this film and the sequel. This makes them the only actors to reprise their roles from the TV show. They completed their contributions over the course of one dubbing day.
A US comic book adaption was published by Dell Comics in 1966, with artwork by Dick Giordano and Sal Trapani. It was subsequently reprinted by Marvel Comics in 1993, as issue 9 of their "Doctor Who Classic Comics" line.
The Daleks were inspired by the Nazis. Yet ironically, the Thals, (the humanoid race who the Daleks want to eliminate from the planet Skaro) are all white, blonde and athletic-looking, similar to the Nazi ideal of the Aryan master race.