Third Doctor See List of non-televised Third Doctor stories. Third Doctor The Third Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television series "Doctor Who". He was portrayed by actor Jon Pertwee. Within the series' narrative, the Doctor is a centuries-old Time Lord alien from the planet Gallifrey who travels in time and space in his TARDIS, frequently with companions. At the end of life, the Doctor can regenerate his body; as a result, his physical appearance and personality change. Pertwee portrays the third such incarnation, a dapper man of action of stark contrast to his
K9 (Doctor Who) Jaeger) in the year 5000. K9 subsequently travelled with the Fourth Doctor (Tom Baker) and Leela (Louise Jameson) as a companion of the Doctor in his adventures in time and space until "The Invasion of Time" (1978). In this serial, K9 decides to remain on the Doctor's home planet of Gallifrey with Leela. Immediately afterwards, "Doctor Who" would introduce a second incarnation of K9, played by the same prop; the last scene of "The Invasion of Time" shows the Doctor unpacking a box labeled "K9 Mk II". Although the first incarnation of K9 does not appear again in televised "Doctor