LOS ANGELES (AP) — Disney movie studio boss Rich Ross is stepping down, a month after the family entertainment giant booked a huge loss on the mega-budget sci-fi movie "John Carter."

Ross, 50, had taken the job just two and a half years ago with a mission to cut costs and develop new hits. He had brought "High School Musical" and "Hannah Montana" to TV audiences as the former head of Disney Channels Worldwide.

But the studio's losses continued under Ross despite major restructuring efforts.

A month ago, Disney booked a $200 million loss on "John Carter," a special-effects-laden movie based on the Edgar Rice Burroughs book series. The movie starring Taylor Kitsch had an estimated budget of $250 million, matching what 20th Century Fox spent on "Avatar."

"John Carter" made only $269 million at box offices worldwide while "Avatar" took in $2.8 billion. After splits with theater owners and marketing expenses, Disney said "John Carter" would cause a studio-wide loss of $80 million to $120 million in the quarter through March.

Ross told staff in a memo Friday that the chairman's role at Walt Disney Studios was no longer right for him.

"The best people need to be in the right jobs, in roles they are passionate about, doing work that leverages the full range of their abilities," he said. "I no longer believe the chairman role is the right professional fit for me."

Ross's resignation is effective immediately. The Walt Disney Co. did not name a successor.

Ross spent much of his early tenure at the studio trying to cut costs and cancel projects that weren't seen as important to the Disney brand.

He shut down the San Francisco-area motion-capture facility used to create "A Christmas Carol," which was run by director Robert Zemeckis. But he let "Mars Needs Moms," the last movie made there, become an epic disaster at theaters in March 2011.

He helped sell the award-winning Miramax label to outside investors in December 2010.

He cut costly or frivolous films from the studio's development slate, such as "20,000 Leagues Under the Sea" and "Wild Hogs 2."

But those efforts were overshadowed by movies that failed to excite audiences, including "Prince of Persia," ''Prom," and even "Winnie the Pooh."

Disney's most successful movies have been made by studios it has bought, including "Toy Story" maker Pixar and Marvel, which will release the much-buzzed "The Avengers" overseas next week.

Disney also distributes movies made by Steven Spielberg's DreamWorks production company, including "War Horse," under its Touchstone brand.

Disney CEO Bob Iger wished Ross well in a statement.

"Rich Ross's creative instincts, business acumen and personal integrity have driven results in key businesses for Disney," Iger said. "I appreciate his countless contributions throughout his entire career at Disney, and expect he will have tremendous success in whatever he chooses to do next."