Sherlock Holmes is an eccentric detective-for-hire who becomes a wanted fugitive in his hunt for Lord Blackwood, while constantly being followed by the presence of Professor Moriarty.
Downey was visiting Joel Silver's offices with his wife, producer Susan Downey, when he learned about the project. Ritchie initially felt Downey was too old for the role because he wanted the film to show a younger Holmes on a learning curve like Batman Begins. Ritchie decided to take a chance on casting him in the role, and Downey told the BBC that "I think me and Guy are well-suited to working together. The more I look into the books, the more fantastic it becomes. Holmes is such a weirdo". Downey also revealed what his wife had to say: "that when you read the description of the guy — quirky and kind of nuts — it could be a description of me". Downey intended to focus more on Holmes' patriotic side and his bohemianism, and felt that his work on Chaplin has prepared him for an English accent. Ritchie feels his accent is "flawless". Both Downey and Ritchie are martial arts enthusiasts, and have been inspired by the Baritsu mentioned in the 1901 story The Adventure of the Empty House. Downey lost weight for the part, because during a chat he had with Chris Martin, Martin recommended that Holmes look "gaunt" and "skinny".
After the death of Irene Adler (See: Sherlock Holmes: A Game of Shadows), Holmes is driven by revenge to solve his case and bring down Moriarty.