Robert Downey Jr. is in final negotiations to don Sherlock Holmes’ cap and pipe in director Guy Ritchie’s big screen adaptation of the Arthur Conan Doyle ethos, according to the Hollywood Reporter.

British director Guy Ritchie is helming the project for Warner Bros. The film is slated for an October 2009 release.

This would be Robert Downey Jr.’s first movie since his magnificent comeback with “Iron Man” earlier this summer. He will play world-famous sleuth Sherlock Holmes as portrayed in an upcoming comic book written by producer Lionel Wigram, per the HR.

In Wigram’s vision, Sherlock Holmes is more adventurous and less “stuffy” than seen in previous screen characterizations. Less known character traits will be brought to the forefront.

Filming starts in the fall. Joel Silver, Wigram, Susan Downey, the actor’s wife, and Dan Lin are producing.

It was through Susan Downey, Silver Pictures executive vice president, that the 43-year-old came across this project, reports the HR. Susan Downey and Joel Silver, who produced Guy Ritchie’s upcoming film “RocknRolla,” were working with the director on “Holmes” and as her actor hubby was in Silver Pictures’ Warner-based offices, he was shown the project and became interested.

Previous movie industry reports concerning Robert Downey Jr. announced the actor was attached to star in DreamWorks’ “Cowboys and Aliens,” a project which promises to make an original mix of two antithetic genres. This film could be released in 2010 but no opening date has been clearly set yet. 

While Ritchie and Downey work on their version of “Holmes,” a rival film will be in the works at Columbia Pictures Sherlock, with Sacha Baron Cohen in the lead role and Will Ferrell as Holmes’ trusted assistant Dr Watson. Judd Apatow is producing the movie, but no director has been announced yet.

Downey next appears in the Ben Stiller-directed comedy “Tropic Thunder,” in August, alongside Stiller, Jack Black and Steve Coogan. In November, he appears in the drama “The Soloist.” Both are distributed by DreamWorks.