What demonic entity is the primary villain of "Green Lantern"?

The primary villain of “Green Lantern” is Parallax. In the 2011 film, Parallax is a massive, space-faring entity that feeds on fear and threatens to consume entire worlds.

The creature was once associated with the Guardians of the Universe, who discovered it after it escaped from the yellow-energy realm of fear. Its appearance as a swirling, cloud-like monster reflects the film’s emphasis on fear as the opposite of willpower, the energy used by Green Lanterns.

Parallax is especially dangerous because fear weakens the Green Lantern Corps. Hal Jordan must overcome his own fear and learn to use the power of willpower effectively before confronting it. The film also links Parallax to Hector Hammond’s transformation, although Hammond is a secondary human antagonist rather than the main villain.

Comic readers may know Parallax differently. In later DC continuity, Parallax is a fear entity that possesses hosts, including Hal Jordan. The film keeps the name and fear-based concept but presents Parallax primarily as a gigantic extraterrestrial antagonist.