Doctor Who, a long-running British science fiction television series, has many creatures and aliens that exist in its fictional universe. Beginning in 1963, the show ran until 1989, at which point it was cancelled. It was later revived in 2005. The series stars its protagonist, the Doctor, an alien who travels through time and space in a ship known as the TARDIS, as well as their travelling companions, as they explore the universe. When the Doctor dies, they are able to undergo a process known as "regeneration", completely changing the Doctor's appearance and personality. Throughout their travels, the Doctor often comes into conflict with various creatures and alien species, with many of them serving as both supporting characters and as antagonists. These creatures are often dubbed "monsters" by fans of the series. This list covers alien races and other fictional creatures from the show's universe, as well as from several of its spin-off series, such as The Sarah Jane Adventures, Torchwood, and Class, in chronological order of their first appearance.

Initially an educational show, the introduction of the Daleks in the show's second story saw Doctor Who gain a ratings spike. More monsters were made to attempt to capitalise off the Daleks' success and subsequently became a larger focus within the series, notably during the period where Patrick Troughton acted as the Second Doctor. Monsters subsequently became incorporated throughout the rest of the show's original run, with concepts and premises for them being inspired by the setting and atmosphere of the current era of the show. Following the show's cancellation in 1989 and its subsequent revival in 2005, monsters once again became a major part of the show, with many returning from its original run.

The initial usage of monsters in the show's original run has been cited by critics as lacking in significant depth, with many monsters described as pure evil "Others" that sought to represent British cultural anxieties. However, as the series has progressed, critics have noted that monsters gained an increased level of character depth that allowed them to be portrayed more sympathetically.

Conception and design During the course of the series, the Doctor encounters many creatures, including alien species, with many of them acting as antagonists. These creatures are often dubbed "monsters" by fans of the series. Author Graham Sleight, in the book The Doctor's Monsters: Meanings of the Monstrous in Doctor Who defines a monster in the context of the show as "a creature of nonhuman appearance that acts in a way that's evil, or at least meant to harm the protagonist and other characters we're meant to be sympathetic with". Despite this, there are many alien species that do not act in an antagonistic manner; one example are the Draconians from the 1973 serial Frontier in Space, who have a distinctive non-human appearance yet are not inherently evil. Races such as these may still be categorised as a "monsters", however. Monsters are often adapted into spin-off media for the series, such as books, audio dramas, and comics, which often expand upon the creatures' backstories and abilities, though these stories often conflict with television series canon. Some monsters, such as the Voord, a mysterious race of black-suited creatures, have entire mythos constructed within spin-off media.

Classic series Doctor Who was originally conceived as an educational show, with the series' format being planned so that it would involve the Doctor going back in time and experiencing important historical events. Early on in the series, however, the production team had no stories ready to be made, which resulted in The Daleks (1963-1964) being put into production. The serial featured the titular alien species, and its inclusion in the series was justified under the show's educational banner as being used to educate about nuclear war and its consequences to children. The Head of Drama at the BBC, Sydney Newman, initially disliked the idea of the Daleks, believing that Doctor Who should have no aliens or monsters. The Daleks, however, were highly popular with audiences, ensuring their return in subsequent stories. As the series' first few seasons progressed, the show's purely historical stories were phased out, being replaced by a format of visiting alien worlds and meeting alien species. Additionally, the Daleks' success led to many attempts at re-creating this popularity with monsters such as the Mechonoids and Voord, though these attempts were largely unsuccessful.

Patrick Troughton's first season on the show as the Second Doctor saw a time of change for the series. The Daleks were expanded upon as antagonists, while the Cybermen, who had debuted in 1966's The Tenth Planet, became recurring antagonists following their debut appearance. The Daleks, whom Terry Nation, their creator, was trying to pitch as part of a television series in America, were written out of the series in 1967's The Evil of the Daleks, resulting in the introduction of several new recurring monsters to fill the gap left in the programme by the Daleks' absence. Troughton's second season saw an expansion of the show's monsters. By this point, the Cybermen were established as one of the series' main antagonists; the Ice Warriors and Yeti similarly were established during this season, becoming major recurring antagonists.

Initially, the show featured very few major invasions of contemporary Earth, but several serials during Troughton's time on the show began to experiment with this format. The success of the Troughton-era invasion serials, as well as a desire to reinvent the show, led to the era of Jon Pertwee's Third Doctor featuring many invasions of Earth. This format had limitations, however, with many of these invasion plots being similar in concept to those of the Quatermass series. Other serials, however, such as the 1970 serial Doctor Who and the Silurians, which introduced the titular monsters as recurring antagonists, focused on more scientific concepts and were more inventive in concept than a "standard" alien invasion story; for example, the Silurians had sympathetic motivations and were not traditional alien invaders, coming from the Earth instead of from space. Creatures with a mostly silver or black and white-based colour scheme, most notably the Cybermen, were phased out as antagonists, with newer antagonists being more colourful and "organic"; this was due to the series swapping to colour television, allowing the latter type of monster to be better realised on-screen. The production team eventually found these invasion stories thematically shallow and overly long, with each serial initially lasting seven episodes each. While the episode counts were decreased to address the length issue, the alien invasion stories were retained and increased in prominence in the show's eighth season. The season's opening serial, 1971's Terror of the Autons, was considered so terrifying by viewers and critics alike as a result of its titular monster that the production team decided to bring back adventures set in outer space, which had previously been avoided in Pertwee's era. The Daleks were also brought back as recurring antagonists.

The first season of actor Tom Baker's era as the Fourth Doctor saw the return of many old antagonists, such as the Daleks, Cybermen, and Sontarans. The production team aimed to make the show more sophisticated, re-vamping the series and giving stories greater depth; this re-invention extended to their returning antagonists. James Chapman stated in the book Inside the TARDIS: The Worlds of Doctor Who that this season served as a reinvention of the series' past while simultaneously shifting away from it, as subsequent seasons saw fewer returning antagonists. Producer Philip Hinchcliffe wanted the show to move away from the alien invasion stories on Earth that had been present in Pertwee's era, wanting a shift to cosmic threats with less absolute goals. Following this season, the show shifted to explorations of deep space, away from Earth-based settings, with many of the new alien creatures, such as the Krynoids and Zygons, being firmly grounded within the genre of horror in their origins. This period of the show was described as "gothic", and featured "oppressive" and "claustrophobic" alien planet designs, and any familiar Earth locations were given darker touches. Monster based horror stories were largely abandoned by the time of the show's sixteenth season, with the stories becoming more comedic instead. This season, dubbed "The Key to Time", largely dropped them due to the "unique" nature of the season.

Led under the tenure of producer John Nathan-Turner, actor Peter Davison's time as the Fifth Doctor saw a shift away from the comedic focus, with the show's twentieth series, its anniversary series, beginning a period of the show bringing back many antagonists from its past. The show's twenty-first series saw further returns of multiple monsters, including the Daleks, Silurians, and Sea Devils. Colin Baker's time as the Sixth Doctor saw the returns of many previously appearing monsters, including the Cybermen and Sontarans. Many of these monster returns in the later years of the show's Classic era were directly tied to prior appearances, with many being direct sequels to prior stories. This was done due to the production team believing fans wanted to see more ties back to the series' past, but contemporary reviews disliked these returns, which alienated fans more than it appealed to them.

Revived series

Following the show's cancellation in 1989 and an aborted revival attempt via a television film in 1996, the show was properly revived in 2005. The revived series was initially headed by writer and showrunner Russell T Davies. Following Davies's departure in 2010, Steven Moffat took over, with Moffat staying on until Chris Chibnall took over as showrunner in 2018. Following Chibnall's tenure, Davies returned to the showrunner role in 2022. The revival changed and reinterpreted the show's setting, particularly in the form of the Last Great Time War, an event that radically shifted the universe's status quo.

Many of the monsters in the revival, unlike in the classic series, focused less on conquering territory. Many are instead attempting to survive and carry on their race, or do not know they are causing harm. One type of story that became prevalent in the show's revival is the "returning monster" story, which saw monsters from the Classic era of the show brought back and revamped; these stories tended to receive much higher press coverage and be more important within the show's narrative. Davies' initial time on the show saw the return of several monsters, who were incorporated and interpreted within the show's revamped mythology. Returning monsters included the Daleks, Cybermen, Sontarans, Nestenes and Autons, and the Macra. Returning monsters often saw their designs altered, striking a balance between "homage and revision". Unlike the Classic era, where these re-appearances hinged on prior episodes, episodes featuring these monsters often paid homage to prior episodes but did not require them to be understood by the show's audience.