The war of words between Mr. Whitmire and Disney was startling, given the outward harmony of the Muppets brand and the fact that when prominent performers are fired, the two sides usually come to terms and agree not to disparage each other. In this case, both Mr. Whitmire and Disney executives say they are fighting to protect the reputation and legacy of a beloved brand.

Mr. Whitmire portrayed Kermit for 27 years in numerous films and television shows and took the puppet all over the world as the Muppets’ pop culture significance expanded: a commencement ceremony, late-night comedy shows and even an episode of “WWE Raw.” Now the actor’s career is in ruins, while the Muppet brand will try to recover with Matt Vogel, a veteran Henson puppeteer, taking over the role.

In a 45-minute interview on Monday, a rarity without a piece of felt on his hand, Mr. Whitmire said that last October he received a phone call from two top Muppets Studio executives, both of whom he declined to name, telling him that he was being let go.

The executives gave two reasons for the decision, Mr. Whitmire recalled.

“They were uncomfortable with the way I had handled giving notes to one of the top creative executives on the series,” Mr. Whitmire said, referring to “The Muppets,” the most recent television revival of the franchise, which aired on ABC for one season, ending in March 2016.

“Nobody was yelling and screaming or using inappropriate language or typing in capitals,” he said. “It was strictly that I was sending detailed notes. I don’t feel that I was, in any way, disrespectful by doing that.”