The poet Robert Browning once wrote that “a man in armor is his armor’s slave.” By that logic, director Jon Favreau is now a free man: Insiders tell Vulture that Favreau has just informed Marvel Studios that he won’t direct a third Iron Man film.

It’s unclear whether the impasse was financial or creative or both. One informed source hears that he was frustrated with Marvel’s urge to stuff more of their in-house heroes into the next film in the wake of The Avengers. In a recent interview with MTV News, Favreau explained that based on his conversations with Marvel Studios executives, he had no clarity as to what a third Iron Man film would even be about. “In theory, Iron Man 3 is going to be a sequel or continuation of Thor, Hulk, Captain America and Avengers,” said Favreau at the time, “This whole world I have no idea what it is. I don’t think they do either, from conversations I’ve had with those guys.”

Still other industry insiders look at Favreau’s growing price tag and speculate that he was getting too expensive for the frugal Marvel and its equally cost-conscious parent company, Disney. In fact, one Hollywood player familiar with Marvel’s playbook theorizes that the company had been pushing a confusing and packed vision of the third film as a tactic to provoke Favreau into leaving the project. Favreau, after all, is said to have received $10 million for the Iron Man sequel; it’s unclear what he’d be seeking for a third film, but reps familiar with these sorts of gross participation deals tell Vulture that he likely would command $12 million to $15 million up front, plus a 15 percent percent of the gross after the film recouped. With star Robert Downey Jr. also participating in the gross (and so far it’s a $1.2 billion global franchise), that’s an enormous amount of cash headed out the door. Disney has got to be protective of their profits for an IM3: It bought Marvel for $4 billion in 2009, and then this October paid Paramount Pictures $115 million for the distribution rights to The Avengers and Iron Man 3 in order to reunite the titles with their parent company.

Regardless of why, we’re told that Marvel quietly began the process of finding a director to replace Favreau last night. But Marvel’s task is complicated by the fact that Downey Jr. has both contractually negotiated director approval and is currently the hottest leading man in Hollywood with first pick of dozens of “go” movies around town.

Favreau will be staying on the Disney lot, at least for now: His next project will be the studio’s Magic Kingdom, about a family trapped in Disneyland and their magical encounters with all sorts of Disney attractions and rides. Marvel currently has no script for a third Iron Man, and while it has no plans to shoot the film until 2012 at the earliest, Marvel execs hope to put a director on the project to guide its development as soon as possible.