In introducing the extended trailer for Sherlock Holmes at Comic-Con, Robert Downey, Jr. said the character, created by Arthur Conan Doyle around 1887, was an intellectual superhero and the first western martial artist.

Downey joked that the reason Holmes hasn't been remade before now was a casting issue, suggesting with a wink that this production solved that problem.

Writer and producer Lional Wigram, who has also produced the last two Harry Potter films, said that his father used to read the Holmes stories to him when he was a child, and had been trying for years to figure out how to do it as a film.

He ended up making a comic book to show how it could be done, and to demonstrate that the Holmes character is "as much a modern character today as he was in Conan Doyle's time."

Downey plays Holmes, Jude Law is Watson, and Canadian actor Rachel McAdams takes on the role of Irene Adler, a love interest and competitor to Holmes. Downey called her a "vixen adventurer".

The story being told in the film, directed by Guy Ritchie, is original. Wigram said he drew heavily on the "Victorian fascination with the occult" and based the antagonist, Mark Strong's Lord Blackwood, on real-life occultist Aleister Crowley.

The key to making this project come off, said Downey, was going back to the source material. "The more we looked into the lexicon of the four novels and the many short stories," he said, "the more we realized Holmes had been misinterpreted."

They were all wary of making a version of Sherlock Holmes that wasn't quite smart enough, he said, and ultimately came up with a new rendition of the character by "changing less than had been changed before."