The Daleks ( (listen) DAH-leks) are a fictional extraterrestrial race of extremely xenophobic mutants principally portrayed in the British science fiction television programme Doctor Who. They were conceived by writer Terry Nation and first appeared in the 1963 Doctor Who serial The Daleks, in shells designed by Raymond Cusick.

Drawing inspiration from the Nazis, Nation portrayed the Daleks as violent, merciless and pitiless cyborg aliens, completely absent of any emotion other than hate, who demand total conformity to the will of the Dalek with the highest authority, and are bent on the conquest of the universe and the extermination of any other forms of life, including other 'impure' Daleks which are deemed inferior for being different to them. Collectively, they are the greatest enemies of Doctor Who's protagonist, the Time Lord known as "the Doctor". During the second year of the original Doctor Who programme (1963–1989), the Daleks developed their own form of time travel. In the beginning of the second Doctor Who TV series that debuted in 2005, it was established that the Daleks had engaged in a Time War against the Time Lords that affected much of the universe and altered parts of history.

In the programme's narrative, the planet Skaro suffered a thousand-year war between two societies: the Kaleds and the Thals. During this time-period, many natives of Skaro became badly mutated by fallout from nuclear weapons and chemical warfare. The Kaled government believed in genetic purity and swore to "exterminate the Thals" for being inferior. Believing his own society was becoming weak and that it was his duty to create a new master race from the ashes of his people, the Kaled scientist Davros genetically modified several Kaleds into squid-like life-forms he called Daleks, removing "weaknesses" such as mercy and sympathy while increasing aggression and survival-instinct. He then integrated them with tank-like robotic shells equipped with advanced technology based on the same life-support system he himself used since being burned and blinded by a nuclear attack. His creations became intent on dominating the universe by enslaving or purging all "inferior" non-Dalek life.

The Daleks are the show's most popular and famous villains and their returns to the series over the decades have often gained media attention. Their frequent declaration "Exterminate!" has become common usage.