Generator Rex is an American science fiction "nanopunk" action animated television series created by Man of Action for Cartoon Network. John Fang of Cartoon Network Studios serves as supervising director. It is inspired by the comic M. Rex, published by Image Comics in 1999. The series premiered in the United States on April 23, 2010, on Cartoon Network. Generator Rex is rated TV-PG. The last episode of the third season had aired on January 3, 2013.

A heroic version of Lex Luthor from an alternate universe appears to recruit the Justice League to help save his Earth from the Crime Syndicate, an evil version of the League. What ensues is the ultimate battle of good versus evil in a war that threatens both planets and, through a devious plan launched by Batman's counterpart Owlman, puts the balance of all existence in peril.