Downey Jr has signed up for a third Iron Man film
Robert Downey Jr and his Iron Man director Jon Favreau are to team up on another another comic-book movie, Cowboys And Aliens.
Downey Jr has been attached to the project, which is being co-written by Lost's executive producer Damon Lindelof, since last summer.
Favreau will direct the sci-fi Western, which pits cowboys and native-Americans against aliens in 19th Century Arizona.
The film is expected to be released in 2011 - a year after Iron Man 2.
Before then, Downey Jr will star in Guy Ritchie's re-telling of the Sherlock Holmes story, due out on Christmas Day.
Favreau will next appear in the comedy Couples Retreat, alongside Vince Vaughn, Jean Reno and Kristen Bell.