Rich Ross resigned as chairman of Walt Disney Studios Friday marking a surprise exit wedged between the company’s staggering $200 million writedown from “John Carter” and the inevitable box office and ancillary coin from Marvel’s “The Avengers.”

The exec alerted staffers in an email Friday morning of his decision to step down, saying: “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. It’s one of the leadership lessons I’ve learned during my career, and it’s something I’ve been giving a great deal of thought to as I look at the challenges and opportunities ahead.”

Word of Ross’ possible departure started spreading late Thursday after the exec began canceling several high-profile meetings, sources told Variety. The former head of Disney Channels Worldwide, Ross was upped to head the film studio by Walt Disney Company chairman and CEO Bob Iger in October 2009.

Already, Marvel Studios topper Kevin Feige is considered to be at the top of lists for job, given his experience in launching new franchises that perform at the box office — “Iron Man,” “Thor,” “Captain America: The First Avenger” — and spin off sequels, TV shows, videogames, toys and other consumer products, while keeping a close eye on overhead and production costs through long-term deals with actors and tax breaks. All are attributes that fit Disney’s mandate from Iger.

Other candidates include DreamWorks co-prexy and CEO Stacey Snider and producer Joe Roth, who once ran Walt Disney Studios from 1994-2000 and is behind billion-dollar blockbuster “Alice in Wonderland,” and the upcoming “Oz: The Great and Powerful” and “Maleficent,” starring Angelina Jolie. Disney production prexy Sean Bailey could also be in the mix, as could “Battleship”-producer Scott Stuber, who has a first-look deal at Universal (which he once ran with Mary Parent, who’s also considered a possibility).

For now, Bailey and studio present Alan Bergman will oversee the film’s slate, which is set for the year and is coming together for 2013.

Though “John Carter” was greenlit by the Dick Cook regime and championed by John Lasseter and other top Pixar Animation Studios brass, Ross is still taking much of the blame for the film’s poor performance at the box office. Film has earned just $269 million worldwide since its release March 9, and $69 million domestically, forcing the studio to take a $200 million writedown before its second quarter earnings are released May 8.

Such a high-profile failure comes at a time when risk-averse parent companies are scrutinizing shrinking slates — Disney’s own internal wrangling over the budget of next year’s “The Lone Ranger” is a prime example — and demonstrating minimal tolerance for misses in the search for franchise hits. That’s put pressure on studio heads to perform more than ever, focusing less on the creative elements of moviemaking and more on the bottomline.

Ross is also smarting from the experimental hiring of Hollywood outsider MT Carney as the studio’s marketing chief in 2010. After a long search, Ross tapped Carney from Madison Avenue, where she ran the New York arm of ad shop Naked Communications; but Carney’s inexperience in marketing tentpole movies was quickly exposed, forcing Ross to replace her in January with Participant Media president Ricky Strauss.

When films fail at the box office, the marketing chief is usually the first to take the blame — and to get the boot. But the studio chief is always second. Bailey, another Ross hire, will continue as the studio’s president of production.

Disney did enjoy some hits under Ross.

The first film he officially greenlit, “Pirates of the Caribbean: On Stranger Tides,” sailed past $1 billion worldwide; “Tangled” surprised many when it was able to attract a broader audience to the female-skewing Rapunzel tale, which earned $591 million globally; and “Cars 2” revved up more than $500 million. “The Muppets” also was relaunched under Ross, with a sequel now in the works.

But there were also flops, most notably “John Carter,” “Prom” and “Mars Needs Moms,” which led to the shuttering of Robert Zemeckis’ production studio ImageMovers Digital.

Upcoming tentpoles greenlit by Ross include Sam Raimi’s “Oz: The Great and Powerful,” Jerry Bruckheimer’s “The Lone Ranger” and “Maleficent.”

Marvel’s “The Avengers,” the first film Disney is releasing since buying the comicbook publisher in 2009 for $4 billion, bows to what’s being predicted as a $150 million domestic opening weekend on May 4. Ross is departing the studio before he can benefit from the film’s expected heroic haul.

“I no longer believe the Chairman role is the right professional fit for me,” Ross said in his written statement. “For that reason, I have made the very difficult decision to step down as Chairman of The Walt Disney Studios, effective today.”

Given Ross’ track record at Disney Channels, which launched franchises like “High School Musical” and “Hannah Montana,” during his tenure, Iger felt the exec could transfer his abilities in launching hits under a tighter budget that could benefit the rest of the conglom’s divisions, from TV, homevid, online, games, theme park attractions and merchandise. When Iger hired Ross, the Disney chief was openly disappointed by the studio’s performance, and wanted to reduce the risk of making movies whose commercial prospects seemed like a gamble.

As a result, Disney is producing fewer films that focus on the Disney family brand, while it relies on Marvel, Pixar and DreamWorks to supply the rest of the studio’s slate.

“For more than a decade, Rich Ross’s creative instincts, business acumen and personal integrity have driven results in key businesses for Disney, redefining success in kids and family entertainment and launching franchises that generate value across our entire company,” Iger said. “I appreciate his countless contributions throughout his entire career at Disney.”