<Li> Actor Jude Law at the 2007 Toronto International Film Festival . Jude Law as Dr. John Watson, Holmes' companion and close friend who is also a surgeon and a veteran of the Second Afghan War . Law's Watson is more like the original character, who was more of a colleague, rather than the bumbling fool that actor Nigel Bruce popularised in the 1930s--40s films . Law previously appeared in the Granada Television series The Adventures of Sherlock Holmes, in an episode based on "The Adventure of Shoscombe Old Place". Being a Holmes fan, Law recognised there was material unexplored in other adaptations and was intrigued by Downey's casting; Law was cast because he had a positive meeting with Downey and concurred the film would have to explore Holmes and Watson's friendship . Downey believed by emphasizing Watson's qualities as a former soldier, a doctor, a womanizer and a gambler, it would make for a more interesting foil for Holmes . Law made a notebook of phrases from the stories to improvise into his dialogue . Ritchie originally envisioned Russell Crowe in the role . </Li> <Li> Mark Strong as Lord Henry Blackwood, an aristocratic serial killer dabbling in the occult to compel others to do his bidding . Having returned after his execution, Blackwood unveils plans to control the British Empire . He is given many supernatural elements to his character, and his presence is usually accompanied by a menacing crow . Strong worked with director Ritchie for the third time and said he appreciates the director's lack of ego and how easy he is to work with . </Li> <Li> Rachel McAdams as Irene Adler, an American femme fatale from New Jersey who outwitted Holmes, as chronicled in Doyle's story "A Scandal in Bohemia". A skilled professional thief, as well as a divorcée, Adler is no longer married to Godfrey Norton and needs Holmes' help for the case . Downey convinced Ritchie to cast McAdams, arguing she would not look too young to be his love interest . In this aspect the film considerably departs from Doyle's original, where Holmes never met Adler again after the one occasion where she outwitted (and greatly impressed) him; the film conversely implies that the two of them met many times and later had an intermittent, hotly consummated love affair . </Li> <Li> Kelly Reilly as Mary Morstan, a governess whom Watson wishes to marry, causing a conflict with Holmes . </Li>

Who plays irene adler in sherlock holmes movie