So, from what I can gather Parallax is an alien parasite that ends up taking over Green Lantern protagonist Hal Jordan (Ryan Reynolds) turning him into some sort of super-villain. There is a lot more on the backstory at Wikipedia and I am sure you have a better and quicker explanation, but before you correct my comic illiteracy in the comments, have a look at the image above which comes from The Daily Blam (via Bleeding Cool) featuring what is said to be a scanned image of the Parallax from the upcoming Green Lantern movie. However, the Bleeding Cool folks seem skeptical as to its legitimacy. Have a look at the DC Comics version of the character below.
