Say what you will about the heroes in a half-shell, but at least one of those guys is a real "Jackass."

Johnny Knoxville lends his voice to sword-wielding fearless leader Leonardo in "Teenage Mutant Ninja Turtles," producer Michael Bay and director Jonathan Liebesman's upcoming adaptation of the classic cartoon, comic book and action figure franchise. Knoxville's Leo voice makes its grand debut in a new trailer for "Ninja Turtles," featuring 30 seconds of non-stop ninja action.

Aside from being an action-packed look at the upcoming "Turtles" movie, complete with a tease for how these characters act and sound, the new trailer shows us more about their origin. We see the Turtles in their infancy, then growing up as youngsters, training for Master Splinter. We even see the film's version of Shredder, a hulking, heavy-metal menace that looks even more roided out than the Super Shredder of "Teenage Mutant Ninja Turtles II: Secret of the Ooze."

"Teenage Mutant Ninja Turtles," starring Megan Fox and Will Arnett, hits theaters on August 8.