
The Doctor is the title character in the long-running BBC science fiction television programme Doctor Who. Since the show's inception in 1963, the character has been portrayed by thirteen lead actors. In the programme, "the Doctor" is the alias assumed by a millennia-old alien called a Time Lord who travels through space and time in the TARDIS, frequently with companions. The transition to each succeeding actor is explained within the show's narrative through the plot device of "regeneration", a biological function of the Time Lord race that allows a change of cellular structure and appearance with recovery following a potentially fatal injury.

The First Doctor is the original incarnation of the Doctor and the initial protagonist of the BBC science fiction television series Doctor Who. He was portrayed by actor William Hartnell.

The Second Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television series Doctor Who. He was portrayed by actor Patrick Troughton.

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 alien Time Lord from the planet Gallifrey who travels in time and space in the TARDIS, frequently with companions. At the end of life, the Doctor regenerates. Consequently, both the physical appearance and personality of the Doctor changes.

The Fourth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television series Doctor Who. He was portrayed by Tom Baker.

The Fifth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television series Doctor Who. He is portrayed by Peter Davison.

The Sixth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television series Doctor Who. He is portrayed by Colin Baker. Although his televisual time on the series was comparatively brief and turbulent, Baker has continued as the Sixth Doctor in Big Finish's range of original Doctor Who audio adventures. Within the series' narrative, the Doctor is a centuries-old alien Time Lord from the planet Gallifrey who travels in time and space in the TARDIS, frequently with companions. At the end of life, the Doctor regenerates; as a result, the physical appearance and personality of the Doctor changes. Baker portrays the sixth such incarnation, an arrogant, flamboyant character in brightly coloured, mismatched clothes whose brash, often patronising personality set him apart from all his previous incarnations.

The Seventh Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television series Doctor Who. He is portrayed by Scottish actor Sylvester McCoy.

The Eighth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television series Doctor Who. He is portrayed by Paul McGann.

The Ninth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme Doctor Who. He is portrayed by Christopher Eccleston during the first series of the show's revival in 2005. Within the series' narrative, the Doctor is a centuries-old alien Time Lord from the planet Gallifrey who travels in time and space in the TARDIS, frequently with companions. At the end of life, the Doctor regenerates; as a result, the physical appearance and personality of the Doctor changes.

The Tenth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme Doctor Who. He is played by David Tennant in three series as well as nine specials. As with previous incarnations of the Doctor, the character has also appeared in other Doctor Who spin-offs.

The Eleventh Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme Doctor Who. He is played by Matt Smith in three series as well as five specials. As with previous incarnations of the Doctor, the character has also appeared in other Doctor Who spin-offs.

The Twelfth Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme Doctor Who. He is portrayed by Scottish actor Peter Capaldi. As with previous incarnations of the Doctor, the character has also appeared in other Doctor Who spin-offs.

The Thirteenth Doctor is the current incarnation of the Doctor, the fictional protagonist of the BBC science fiction television programme Doctor Who. She is portrayed by English actress Jodie Whittaker, the first woman to play the character in the series.

Dr. Who is a character based on the Doctor, the protagonist featuring in the long-running BBC science fiction television series Doctor Who.

The Fugitive Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme Doctor Who. She is portrayed by the English actor Jo Martin, the first person of colour to play the role. It is unknown where this incarnation falls within the show's fictional chronology.

The Other is a fictional character in the British science fiction franchise Doctor Who. A legendary figure in Time Lord history, the Other was only alluded to in the television series, but is featured several times in spin-off media based on the programme.

The Shalka Doctor is the common fan name given to the character that appeared as an alternative incarnation of the Doctor in the flash-animated serial Scream of the Shalka in 2003 and the later short story The Feast of the Stone which were based on the British science fiction television series, Doctor Who. He was voiced by the actor Richard E. Grant.

The Valeyard is a fictional character from the long-running British science fiction television series, Doctor Who. He is described by the Master as an amalgamation of the Doctor's darker sides from between his twelfth and final incarnations. In the serial The Trial of a Time Lord, comprising the whole of Season 23 of the series, the High Council of the Time Lords appoint the Valeyard as prosecutor at the Sixth Doctor's trial, hoping to have him executed and thereby remove the sole witness to their near destruction of life on Earth.

The War Doctor is an incarnation of the Doctor, the protagonist of the BBC science fiction television programme Doctor Who. He was portrayed by the English actor John Hurt. Although he precedes Christopher Eccleston's Ninth Doctor in the show's fictional chronology, his first onscreen appearance came eight years after Eccleston's; the War Doctor was retroactively created by showrunner Steven Moffat for productions celebrating the show's 50th anniversary.