"Villain of the week" (or, depending on genre, "monster of the week", "freak of the week", "alien of the week", or "dinosaur of the week") is an antagonist that only appears in one episode of a multi-episode work of fiction, commonly British, American, and Japanese genre-based television series. As many shows of this type air episodes weekly at a rate of ten to twenty new episodes per year, there is often a new antagonist in the plot of each week's episode. The main characters usually confront and vanquish these characters, often never encountering them again.

Shows that use such characters include Doctor Who, Supernatural, Primeval, Grimm, Charmed,^[1] Smallville,^[2] and Scooby-Doo.^[3] Some series alternate between using such antagonists and furthering the series' ongoing plotlines (as in Buffy the Vampire Slayer,^[4] Supernatural,^[2] Fringe,^[5] and The X-Files),^[6][7] while others use these one-time foes as pawns of the recurring adversaries (as in Kamen Rider,^[8] Sailor Moon,^[9] the Ultra series and Super Sentai^[10] and its American equivalent, Power Rangers).^[11][12]

In some cases, these villains return reformed in later episodes, becoming invaluable allies or gaining a larger role in the story.

"Villain of the week" plotlines are attractive to syndicators, as it means that episodes can be rerun in any order and do not need to be aired in sequence as serials with continuing storylines do.

• Big Bad
• Plot device

• Clements, Jonathan; McCarthy, Helen (2015). The Anime Encyclopedia, 3rd Revised Edition: A Century of Japanese Animation. Stone Bridge Press. ISBN 9781611720181.