For those of you out there who didn't already know that 'The Avengers' director Joss Whedon was also a superhero, actors Ruffalo, Downey and Jackson testify

Mark Ruffalo, Samuel L. Jackson, Robert Downey Jr., Chris Hemsworth and other stars of the hit superhero extravaganza, The Avengers, directed by Joss Whedon, are telling fans everywhere what small-screen devotees of Whedon shows like Firefly, Buffy the Vampire Slayer, Dollhouse, Angel and Dr. Horrible's Sing-Along Blog, have known for years: that Joss Whedon is a superhero of sorts as well.

Now that Whedon, whose rewrites of The Avengers made it the $1.5-billion success it's become, is a household name, it's important that his new, more mainstream fans know just how cool he is. "He's such a great collaborator," raved Ruffalo, who played the Hulk in Marvel's take on The Avengers. "He knows the genre so well," Ruffalo said, reports the Los Angeles Times. "He's so expansive in his understanding of a very, very complex story. We worked very closely on this version of Bruce Banner, and it was just — I just love the guy. Had a great time with him. He's so smart. He's hilarious. He's got a great sense of humor. He writes in his completely own style. And he balances humor and action and real drama and mythology — he's perfect for this."

How I Met Your Mother's Cobie Smulders, who plays S.H.I.E.L.D. agent Maria Hill in the flick and has known Whedon for years through her onscreen relationships with Alyson Hannigan, one of the main Buffy the Vampire Slayer stars, and Neil Patrick Harris, a.k.a. "Dr. Horrible," also couldn't keep quiet about the "genius" behind the superhero sensation. "I was so excited that I got to work with him on [Avengers]," Smulders said. "I was quite nervous, and I was very grateful and extremely happy to have him there and in my corner. He was very kind to me and very much put me at ease, and he was great."

Even onscreen legend in his own right, Jackson (Nick Fury in The Avengers), sang Whedon's praises, crediting the director with knowing how to make the superhero characters "understand that yeah, you're all great individually, but think of how much greater you'd be as a unit."

One thing Tom Hiddleston and quintessential Avengers villain Loki understands about Whedon is his incredible range. "He's a Shakespearean, like he's a closet Shakespeare geek," Hiddleston said. "The first time I ever met Joss, he came to see me in London in a production of Othello …. So the reason that I'm in this film is because he saw me doing Shakespeare."

And, as far as superheroes go, Downey may have played one in the form of Tony Stark since 2008, when Jon Favreau directed Iron Man, but that doesn't mean he can't have his own. "The guy's my hero," he said. "He should be yours."

Marvel will next follow up with superhero movie sequels Iron Man 3, Captain America 2, Thor: The Dark World, a television series inspired by the S.H.I.E.L.D. operation and, of course, an as-yet unnamed sequel to The Avengers, which will be helmed by Whedon.

True to Hiddleston's assessment, Whedon will next release his version of Shakespeare's Much Ado About Nothing, starring some of his usual suspects from small and big screens, Amy Acker (Angel, The Cabin in the Woods), Alexis Denisof (Angel), Nathan Fillion (Firefly) and Clark Gregg (The Avengers), set to hit theaters later this year.

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