The Doctor (Doctor Who) footage. Tom Baker did reappear, but as "the Curator", an ambiguously different character who he was not credited for playing. A voice actor, John Guilor, recorded a line of audio impersonating the First Doctor, for which he was credited as "Voice Over Artist". In other multi-Doctor stories, the multiple actors are all credited as "The Doctor", the exception being "The Three Doctors" (1972–73), which credited William Hartnell, Patrick Troughton and Jon Pertwee as "Doctor Who" as the 1972 serial preceded the practice of crediting the character as "The Doctor". In "Human Nature" (2007), the plot involves the Tenth Doctor altering
The Master (Doctor Who) stopped by the Doctor. The Master has featured in spin-offs of the series, which are of unclear canonicity and may not take place in the same continuity. The Master in these stories is, nevertheless, recognisably the same character. One of the most notable of these other appearances is David A. McIntee's "Master trilogy" of novels comprising "The Dark Path" and "First Frontier" in the Virgin Publishing lines and "The Face of the Enemy" for BBC Books, and the "Doctor Who" radio dramas produced by Big Finish Productions, in which Geoffrey Beevers has reprised the role, with a new incarnation being