The author of the book read by the Doctor, "The Origins of the Universe", is Oolon Coluphid. According to script editor Douglas Adams' "The Hitchhiker's Guide to the Galaxy", Oolon Coluphid is the author of the trilogy of philosophical blockbusters "Where God Went Wrong", "Some More of God's Greatest Mistakes", and "Who Is This God Person Anyway?".
This was the last Doctor Who (1963) serial to be written by Terry Nation. However, according to director Ken Grieve, script editor Douglas Adams wrote 98% of the serial (for which he was uncredited).
Mary Tamm was unable to reprise her role as Romana for a regeneration scene due to pregnancy. She would have done so if asked, but she wasn't.
Tim Barlow, who plays Tyssan, was partially deaf, but could lip-read and ran a school for deaf actors.
Parts of the Dalek slaves' costumes were recycled from previous aliens - for example, one wears the costume (but not the mask) of a Draconian, another the trousers from an SV robot ("The Robots of Death"), another has the head of a humanoid-form Axon, and another is wearing a blue Morestran spacesuit.