A villainous protagonist is a character who is the central focus of a story, yet does not have the traditional "heroic" qualities of a classic protagonist. In short, these are the villains who are the main characters of their own stories. Should they have heroic qualities, the audience commonly nickname them "anti-heroes". Their opposites are heroic antagonists.

There can be more than one villainous protagonist in a same story, but each one has to share the same amount of screen time in order to qualify. In Video games, any playable character can qualify. Also, former protagonists who became antagonists (usually due to a tragic event in their life) can also be included, given that they played a large part in the story, even if they no longer function as heroes.

Some can be falsely seen as the "hero", as they are seen on the cover of the movie/book/game/whatever, and therefore, the viewer/reader/player is being lured to believe that the character is the main hero of the story, while they are in fact the main villain (e.g. Spunky).

Good examples of protagonist villains include Caillou from GoAnimate and the Caillou the Grownup series, Vergomoth from The Velvet King, Mario from SMG4, and Joy from Outside In.

These characters are rarely Complete Monsters, because it is very unlikely and odd for a leading character to actually be that evil. In addition, protagonists usually set the villainy standards in their story. However, protagonists can still be Complete Monsters if they have no redeeming qualities and if the characters around them are visibly distressed or repulsed by their actions, thus meaning that they stand out from the rest (e.g. Pedro Rezende, Dimentio, SpongeBob SquarePants, King Stiron, Chara and THOUGHT). In addition, horror works and exploitative medias often feature purely evil protagonists who are meant to be feared as mascots of their own franchise.