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 Doctor (Doctor Who) that time was that regeneration had turned back the Doctor's clock, making him younger both in appearance and in biological age. Since the Doctor's age had never previously been given, 450 Earth years became a starting point onto which further years would be progressively added as the series continued and the character lived out his further incarnations. The Third Doctor implied in "Doctor Who and the Silurians" (1970) and in "The Mind of Evil" (1971) that he had a lifetime that covered "several thousand years". While the Doctor's age has never been a known quantity, these numbers are the most