Batman will always be inspired to fight crime by the death of his parents, Spiderman will always gain his powers after being bitten by a rare arachnid, and the Teenage Mutant Ninja Turtles will always be … well, teenage mutants. Anger has erupted over a bid by Michael Bay to change the origins story of the much-loved heroes in a halfshell in a forthcoming film, with the voice actor who played Michelangelo in the original films the latest to join the chorus of disapproval.

After fans took to Twitter and Facebook to vent anger about Bay's proposals to change the turtles to "lovable aliens" rather than mutants who gain anthropomorphic powers after encountering mysterious radioactive ooze, voice actor Robbie Rist accused the Transformers director of "sodomising" the combative reptiles.

"You probably don't know me but I did some voice work on the first set of movies that you are starting to talk about sodomising," wrote Rist in an open letter to Bay. "I know believing in mutated talking turtles is kinda silly to begin with but am I supposed to be led to believe there are ninjas from another planet? The rape of our childhood memories continues ..."

Rist's comments followed Bay's revelation that the new turtles would arrive from another planet. He said: "These turtles are from an alien race, and they're going to be tough, edgy, funny, and completely lovable."

Fan ire appears to have ruffled the feathers of the famously outspoken film-maker, who is producing the new movie through his Platinum Dunes company. He has now issued a response to concerns over the change to the turtle's origins story in which he tells critics to relax.

"Fans need to take a breath, and chill," Bay's statement said. "They have not read the script. Our team is working closely with one of the original creators of Ninja Turtles to help expand and give a more complex back story.

"Relax, we are including everything that made you become fans in the first place. We are just building a richer world."

The latest Teenage Mutant Ninja Turtles film, which seems likely to be titled simply Ninja Turtles, will most likely be directed by Battle Los Angeles' Jonathan Liebesman. It will be the fifth film to star the characters, who sprang to life in a black and white 1984 comic book series before graduating to film and TV. Named after famous renaissance painters, Leonardo, Raphael, Michelangelo and Donatello made their big screen debut in 1990's Teenage Mutant Ninja Turtles (one of the most profitable independent movies ever) and appeared in two further live action films, in 1991 and 1993, before switching to CGI animation for 2007's TMNT. The latest iteration, which will be based on a screenplay from Mission: Impossible – Ghost Protocol's Josh Appelbaum and Andre Nemec, reportedly marks a return to live action.