Robert Downey Jr. is on the verge of signing on the dotted line to star in DreamWorks/Universal's Cowboys & Aliens, a film that has blockbuster potential for 2010. The project has been in development at various studios for the past 10 years, but with Downey’s signature, it finally looks like all systems go.

The film is based on a graphic novel and revolves around an Old West battle between the Apache and Western settlers, including a former Union Army gunslinger named Zeke Jackson (Downey), that is interrupted by a spaceship crashing into the prairie near Silver City, Ariz. The story draws a parallel between the American imperialist drive to conquer the Indians with its advanced technology and the aliens' assault on Earthlings, who must join together to survive the invaders' attack.

Imagine Entertainment partners Brian Grazer and Ron Howard are producing, along with DreamWorks heads Steven Spielberg, Alex Kurtzman and Roberto Orci. Platinum Studios chairman and CEO Scott Mitchell Rosenberg also will produce. This is Downey's first signing since his stock sky-rocketed on the strength of Iron Man. He’ll next be seen in the comedy Tropic Thunder in August, and the drama The Soloist, which will be released in November.