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Robert Downey Jr. in the Iron Man Avengers franchises
Before Downey signed on to play Tony Stark and secured his path to becoming the world's most bankable action star, he was — by his own admission — an unreliable actor and a box office failure. Not even 10 years ago, who would have pegged the fringe Brat Packer and Chaplin Oscar nominee to lead the charge on a series of Marvel franchises (just one film of which, The Avengers, personally earned him $50 million) that show no signs of slowing down? Nobody, we're guessing. And yet that's what Iron Man did for Downey, making him professionally unbeatable just like Stark's alter ego.
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Morgan Freeman, Helen Mirren, and John Malkovich in RED and RED 2
After originating the role of Alex Cross in Kiss the Girls and Along Came a Spider, Freeman — who didn't return for RED 2 after his character was killed off at the end of the first film — oddly was the likeliest of this trio to play a ''Retired and Extremely Dangerous'' CIA assassin. Based on his prolific career, the mannered Malkovich would rank next after playing a CIA agent in 1993's In the Line of Fire. Least likely to rock this role? All bets would have been on Mirren, who was better known for waving off Brits, instead of baddies, as The Queen's Elizabeth II. And yet it was Mirren who turned out to be the most effective actioner of the bunch. Then again, Freeman, Malkovich, and Mirren's fourth co-star Bruce Willis also once found himself on the receiving end of doubts — when he signed up for Die Hard.
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Tyler Perry in Alex Cross
Better known for strapping on Madea's stuffed bra than a gun holster, the funnyman mogul got ultra-serious for this grisly murder mystery.
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Vanilla Ice in Cool As Ice
Note from the future to Rob Van Winkle: All right, stop! Do not collaborate with filmmakers, and please listen — just because you can wax chumps like a candle lyrically doesn't mean you should attempt to do so on celluloid. Critical and commercial reception will be too cold, too cold. Word to ya mutha.
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Saoirse Ronan in Hanna
At about 100 pounds soaking wet, Ronan (a.k.a. that little twerp from Atonement) didn't exactly come off as a killing machine. But her sinewy frame (good for fitting into hiding places) and her deceptively innocent appearance surprisingly worked.
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Anthony Michael Hall in Out of Bounds
Farmer Ted from Sixteen Candles kicking tail and taking names? The Breakfast Club's Brian banging down doors? Hall's transition from featherweight geek to Man on a Mission probably sounds as unlikely to you as it did to audiences back in the mid-'80s. This botched attempt at reinvention was as awkward as...well...puberty.
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Meryl Streep in The River Wild
Imagine that meeting: ''Ren McCormack hijacks a raft! We'll need a real heavy hitter to take him out. Somebody get Meryl on the phone!'' Regardless of the only-in-Hollywood machinations it must have taken to get this project to the light of day, the film's surge to the top of the box office in its opening weekend proved once again that La Streep can do anything she sets her mind to.
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Kurt Thomas in Gymkata
The former Olympian certainly had the athletic prowess, but did all the action sequences have to be gymnastics-based? I'm sorry, but there is no way to make the pommel horse look threatening.
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Michael Keaton in Batman
Maybe it was his career in comedies and his fidgety, tic-filled persona. Perhaps it was his slight frame and utter lack of suave. Either way, nothing about Keaton screamed, ''Put this man in a rubber suit!'' In fact, when Tim Burton (Keaton's director on Beetlejuice) cast Mr. Mom as the Caped Crusader, comic fans wrote thousands of letters of protest to Warner Bros. That said, George Clooney can attest that looking the part doesn't guarantee success.
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Pamela Anderson in Barb Wire
Though Anderson had been been saving lives on Baywatch for years before this comic book adaptation came along, it seemed a safe bet that Anderson's...ummmmm...flotation devices might be more useful in the water than in a gunfight. Really, would any super-villain worth his salt allow himself be thwarted by a pleather-clad sex kitten who sounds like she just took a shot of helium?
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Seth Rogen in Green Hornet
The schlumpy Canadian import made his name as a stoner in everything from Freaks and Geeks to Knocked Up and Pineapple Express. He was so out-of-shape when filming scenes for the low-action comedy Observe and Report that he admitted to getting winded doing the most basic stunts. Though he slimmed down for Hornet, his turn as a comic book super hero was mostly met with lethargy and giggles.
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John Stamos in Born To Ride
The face of a Greek god and a feathered coiffure do not an action star a-make. At the peak of his success as Full House's Elvis-obsessed Uncle Jesse Katsopolis, Stamos tried to leverage his fame to get into the action game. Quoth the audience: ''No thank you. No thank you very much.''
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Tobey Maguire in Spider-Man
Could a sensitive soul transform himself into a pillar of strength? That was the worry when the Pleasantville alum signed on to play Peter Parker. Fans knew he could convey Peter's geek streak, but, despite buffing up nicely, he never fully mastered Spidey's swagger. Witness: This truly unfortunate Tony Manero homage from Spider-Man 3.
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Drew Barrymore, Madeleine Stowe, Mary Stuart Masterson, and Andie MacDowell in Bad Girls
We wanted ''Bad Girls'' of the toot-toot-beep-beep variety; instead we got this motley crew of ingenues stumbling into the OK Corral. Madeleine Stowe has since proven herself to be a formidable string-puller on Revenge, but essentially everyone on this list made her mark playing the female actress pigeonhole of victim, sex object, or some combination thereof.
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Paul Bettany in Priest
His imaginary friend role in A Beautiful Mind was eliminated by sheer will power, and his turn as an overzealous monk in The Da Vinci Code proved Bettany might be best equipped to beat up himself. After the middling success of 2010's Legion, the British beanpole stepped back into the vestments in hopes that lightning would strike twice. Facing off against Thor's second week at the box office, he didn't stand a chance.
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Corey Haim in Prayer for the Rollerboys
Haim gained international fame by landing punchlines, not punches. Unfortunately, Rollerboys had more of the former (unintentionally).