The Doctor (Doctor Who) Time Lords a fixed number of twelve regenerations, meaning that every Time Lord had a total of thirteen incarnations including the original. The plot of "The Time of the Doctor" involves the Doctor receiving a new cycle of regenerations from the Time Lords before his expected demise, triggering the regeneration into the Twelfth Doctor, played by Peter Capaldi. The origins of the programme were explored in the docudrama "An Adventure in Space and Time" as part of the 50th anniversary celebrations of "Doctor Who", which starred David Bradley as William Hartnell. Although Time Lords resemble humans, their physiology differs in
Dreamland (Doctor Who) and is married to David Tennant who played the tenth Doctor. She portrayed Tanya Webster in the audio drama "Red Dawn" with Davison reprising his role as the Fifth Doctor, and she narrated the Tenth Doctor audio-book "Snowglobe 7". Lisa Bowerman (Saruba Velak) played the Cheetah Person Karra in the 1989 "Doctor Who" serial "Survival" (the last serial of the classic series to be broadcast). Since 1998, she has also played Bernice Summerfield in the ongoing Big Finish audio drama series and in occasional "Doctor Who" audio stories. Veteran actor David Warner has also appeared in numerous Big Finish audio