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

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. Preceded in regeneration by the Fourth Doctor (Tom Baker), he is followed by the Sixth Doctor (Colin Baker).

Davison portrays the Fifth Doctor as having a vulnerable side and a tendency towards indecisiveness, dressed as a boyish Edwardian cricketer. He travelled with a host of companions, including boy genius Adric (Matthew Waterhouse), alien aristocrat Nyssa (Sarah Sutton) and Australian flight attendant Tegan Jovanka (Janet Fielding), who had travelled with his previous incarnation. He also shared later adventures alongside devious schoolboy Vislor Turlough (Mark Strickson) and American college student Peri Brown (Nicola Bryant).

After Tom Baker, the Fourth Doctor, and the BBC had announced that he was leaving the role, the show's producers decided that the next Doctor was to be played by someone who presented something of a physical contrast to Baker and by an actor who was already firmly established in the British public's mind. Peter Davison was chosen due to his high profile role as Tristan Farnon in the BBC series All Creatures Great and Small which had Doctor Who producer John Nathan-Turner as line producer. Davison, who is of half Afro-Guyanese descent, has been credited as the first mixed-race actor to portray the character.

The Fifth Doctor's era was notable for a "back to the basics" attitude, in which "silly" humour (and, to an extent, horror) was kept to a minimum, and more scientific accuracy was encouraged by the producer, John Nathan-Turner. It was, at times, a darker and grittier series, in part for seeing the death of one of his companions, Adric. It was also notable for the reintroduction of many of the Time Lord's enemies, such as the Master, Cybermen, Omega, the Black and White Guardians, and the Silurians.

The Fourth Doctor was seriously injured after falling off the Pharos Project Radio Telescope so he merged with a future incarnation of himself called the Watcher and regenerated into his new youthful fifth incarnation. The regeneration was difficult, and nearly failed, with the Doctor briefly taking on personality aspects from his four previous incarnations. After recovering in the fictional city Castrovalva, he continued his travels with Adric, Tegan Jovanka and Nyssa. Initially his travels centred on getting Tegan back to Heathrow Airport in time for her first day as an airhostess, but the TARDIS repeatedly missed this destination and Tegan eventually decided to stay in the TARDIS. After trips to the future and the past encountering villains such as Monarch and the Mara, the Fifth Doctor was confronted with tragedy when Adric died trying to stop a space freighter from crashing into prehistoric Earth (Earthshock).

Following Adric's death, the TARDIS accidentally arrived at Heathrow airport (Time-Flight). Here the Doctor and Nyssa left Tegan assuming she would want to stay. The Doctor and Nyssa then travelled together for an unspecified amount of time before the renegade Time Lord Omega, attempting to return to the universe, temporally bonded himself to the Doctor (Arc of Infinity). Faced with this threat, the Time Lords were forced to attempt executing the Doctor, but he eventually tracked Omega to Amsterdam where he defeated him and re-encountered Tegan, who having now lost her job, had no second thoughts about rejoining the TARDIS crew.

When the Doctor met a new companion, an alien boy stranded on Earth by the name of Vislor Turlough, he did not know that Turlough had been commissioned by the Black Guardian to kill him. Soon after, Nyssa left to help cure Lazar's Disease on the space station Terminus. After meeting the entities known as Eternals racing in yacht-like spacecraft for the prize of "Enlightenment", Turlough broke free from the Black Guardian's influence, and continued to travel with the Doctor and Tegan. Landing in the reign of King John (The King's Demons), the crew again encountered the Master, who was using a shape-shifting robot Kamelion to impersonate the King. However, the Doctor helped Kamelion to regain his free will and the robot joined him in his travels, although he rarely left the TARDIS. The Doctor met three of his previous incarnations when they were summoned to the Death Zone on Gallifrey by president Borusa, who was attempting to gain Rassilon's secret of immortality.