...no one expected Teenage Mutant Ninja Turtles to hit big when it opened 12 years ago.

Many a comic-book hero is derived from weird phenomena (c’mon, a spider-man?), but Peter Parker himself would have giggled at a quartet of irradiated, crime-fighting shell dwellers. Director Steve Barron and cocreators Peter Laird and Kevin Eastman, however, got the last laugh when New Line Cinema’s $15 million Teenage Mutant Ninja Turtles opened on March 30, 1990, and went on to gross $200 million worldwide — a record for an independent film at that time.

Turtles’ unlikely triumph left Hollywood shell-shocked. But success was nothing new for kung-fu turtles Leonardo, Donatello, Raphael, and Michaelangelo. The foursome had hatched in the minds of comic-book writer-illustrators Eastman and Laird, whose 1983 brainstorm — and $1,200 investment — resulted in the first self-published issue of TMNT. It wasn’t long before kid-TV execs saw green in the turtles and created a syndicated animated series, which aired from 1987 to 1990. But for the film to be a success, it had to appeal to both hardcore comic fans and prepubescent TV fans alike.

For starters, music video vet Barron traded the cartoon’s cheery hues for slightly darker city streets and sewers. Some parents complained that the PG-rated movie was too violent, but the filmmakers aimed to keep it young at heart. ”I looked at it and went ‘Gee, it would be a cute movie for the kids!”’ recalls Corey Feldman, who voiced Donatello in the film. ”It looked pretty schlocky, too…[but] like good, clean family fun.” It didn’t hurt that Muppet master Jim Henson led the hurried design and operation of the turtles, which were played by actors in intricate suits. Those same outfits broke down often over the course of the two-month filming. ”It was just…a very tough shoot,” Barron said.

It was also a tough sell to the many critics who’d lived happily without ninja turtles up until the film’s release. In his two-and-a-half-star review, Roger Ebert wrote that he ”did not walk into [the theater] with a light step and a heart that sang.” But plenty of fans did, and they propelled the film to a $25.4 million opening weekend. Teenage Mutant Ninja Turtles would gross more than $135 million domestically and spawn two sequels.

There’s still life to be found in those shells. Even though a proposed CGI feature film hasn’t gotten off the ground, a fresh comic is on stands and a new animated series is in the works. ”Whatever it is that sparked everybody’s imagination obviously remains,” says Feldman. Just as there are people who grew up on Spidey, we’ll be entrusting our futures to kids raised in the shadow of four feisty turtles. Cowabunga, indeed.