Passage: Ideas for a film based on the Avengers began in 2003, with Avi Arad, the CEO of Marvel Studios, first announcing plans to develop the film in April 2005, after Marvel Enterprises declared independence by allying with Merrill Lynch to produce a slate of films that would be distributed by Paramount Pictures. Marvel discussed their plans in a brief presentation to Wall Street analysts; the studio's intention was to release individual films for the main characters—to establish their identities and familiarize audiences with them—before merging the characters together in a crossover film. Screenwriter Zak Penn, who wrote The Incredible Hulk (2008), became attached to the film in 2006, and was hired by Marvel Studios to write the film in June 2007. In the wake of the 2007–2008 Writers Guild of America strike, Marvel negotiated with the Writers Guild of America to ensure that it could create films based on its comic book counterparts, including Captain America, Ant-Man and The Avengers. After the successful release of Iron Man (2008) in May, the company set a July 2011 release date for The Avengers. In September 2008, Marvel Studios reached an agreement with Paramount—an extension of a previous partnership—which gave the company distribution rights for five future Marvel films.Casting began in October 2008 with Downey's signing. Though Don Cheadle was also reported to be reprising his Iron Man 2 role of War Machine for The Avengers, he later stated that he did not think the character would appear in the film. At the same time, two major prospects occurred for Marvel: Jon Favreau was brought in as an executive producer for the film, and the company signed a long-term lease with Raleigh Studios to produce three other big-budget films—Iron Man 2, Thor (2011), and Captain America: The First Avenger (2011)—at their Manhattan Beach, California complex. Lou Ferrigno, who voiced Hulk in The Incredible Hulk, stated that he would be involved in the film. In February 2009, Samuel L. Jackson signed a nine-picture deal with...

Question: When did casting begin?
September 2008