By Ronald Grover and Lisa Richwine

LOS ANGELES (Reuters) - Rich Ross, chairman of Walt Disney Co's movie studio, stepped down after a two-year stint that included the release of "John Carter," one of the biggest flops in recent Hollywood history.

Ross, named to the job in October 2009, was never able to duplicate the success he enjoyed as president of the Disney Channel, where he was credited with creating monster franchises that included "High School Musical" and "Hannah Montana."

"I no longer believe that the Chairman role is the right professional fit for me," Ross told his staff in an email.

Disney will not immediately name a new head for its studio, a source familiar with the matter said.

As the company's studio chief, Ross approved production of "John Carter," an expensive science-fiction epic whose development had started years earlier. The film's costs eventually ballooned to more than $250 million.

Disney said in March it expected the film to lose about $200 million, and to saddle its studio with $80 million to $120 million in operating losses.

Ross joined Disney Channel in 1996 as a programming and production executive and was promoted to president of the cable channel in 2004. As studio head, he replaced long-time chairman Dick Cook, who was forced out by Disney CEO Bob Iger.

Two weeks before his departure, Ross hosted a lavish Hollywood premiere for "The Avengers," a big-budget special effects film featuring action stars from Disney's Marvel subsidiary. The film is expected to be one of the summer's biggest hits.

(Reporting By Ronald Grover; Editing by Peter Lauria and Lisa Von Ahn)