A Dalek ( , ) is a member of a fictional extraterrestrial race of mutants from the British science fiction television series Doctor Who. Daleks are organisms from the planet Skaro, integrated within a tank-like mechanical casing. The resulting creatures are a powerful race bent on universal conquest and domination, utterly without pity, compassion or remorse (as all of their emotions were removed except hate). They are also, collectively, the greatest extraterrestrial enemies of the Time Lord known as the Doctor. Their most famous catchphrase is "EX-TER-MI-NATE!", with each syllable individually screeched in a frantic electronic voice ().

The Daleks were created by writer Terry Nation and designed by BBC designer Raymond Cusick. They were introduced in December 1963 in the second Doctor Who serial. They became an immediate hit with viewers, featuring in many subsequent serials and two 1960s motion pictures. They have become synonymous with Doctor Who, and their behaviour and catchphrases are part of British popular culture. "Hiding behind the sofa whenever the Daleks appear" has been cited as an essential element of British cultural identity, and in a 2008 survey, 9 out of 10 British children were able to identify a Dalek correctly.

The word "Dalek" has entered the Oxford English Dictionary and other major dictionaries; the Collins Dictionary defines it rather broadly as "any of a set of fictional robot-like creations that are aggressive, mobile, and produce rasping staccato speech". Although no etymology has been attributed to their name, "Dalek" sounds like the Norwegian word "dårlig", which means "bad" or "evil". It is also a trademark, having first been registered by the BBC in 1964 to protect its lucrative range of Dalek merchandise.

The term is sometimes used metaphorically to describe people, usually figures of authority, who act like robots unable to break from their programming. John Birt, the Director-General of the BBC from 1992 to 2000, was publicly called a "croak-voiced Dalek" by playwright Dennis Potter in the MacTaggart Lecture at the 1993 Edinburgh Television Festival. The Daleks appeared on a postage stamp celebrating British popular culture in 1999, photographed by Lord Snowdon.