Dramatic movie transformations

After transforming himself once to play FBI agent Richie DiMaso in American Hustle, rumour has it Hollywood pretty boy Bradley Cooper has undergone another dramatic change for upcoming film American Sniper.

Cooper has reportedly grown a beard and gained around 40 pounds of muscle mass to tell the true life story of Navy SEAL Chris Kyle in the Clint Eastwood project. Over the course of his 10 year career, Kyle notched up 150 confirmed kills.

Co-star Eric Close told E! News: “He put on like 40 pounds [18.1 kg]. He's really been working hard. He looks great. He's really taken on this character… He really takes this story personally and wants to do an honourable job for Chris' memory and for his family.”

Of course, going through a dramatic physical transformation for a role is nothing new in Hollywood - though some shock an audience more than others. Here are just some of the dedicated actors who've undergone huge changes for a part…

Tom Hardy for Rocketman
According to reports, Tom Hardy is set to bulk up once more for his new role as Elton John in upcoming biopic, Rocketman.

Of course the actor's no stranger to dramatic weight gain for a role, having done it previously for Bronson and to play Bane in The Dark Knight Rises. But insiders reckon it'll be tough for the actor this time around.

A source told The Mirror: "It is no surprise Elton would be happy with someone who looks like Tom playing him but it might be a challenge. Hardy is a heartthrob, it will be quite a stretch to make him look like Elton but he is a professional so putting on weight and changing his hair will not be an issue."

Jake Gyllenhaal for Nightcrawler
Many were shocked to see Jake Gyllenhall looking gaunt on the red carpet earlier this month. Having dropped 20lbs for his role as a reporter in upcoming crime drama Nightcrawler, the actor said it was just part of his process.

"It's not different than getting into character for anything," Gyllenhaal explained to US Weekly. "It's more about believing where you are and being present where you are. Who's to say what the process is? I have a strange one … but I love what I do."

Chris Pratt for Guardians of the Galaxy
Those used to seeing funnyman Chris Pratt take it easy in Parks and Recreation might get a surprise when they finally see the Star-Lord actor on the big screen in Guardians of the Galaxy.

The actor has shared pictures of his newly toned physique on Instagram, attributing it to six months off the beer. Pratt had previously gotten in to shape to play a Navy Seal in Zero Dark Thirty before gaining 60 pounds for comedy Starbuck.

Natalie Portman for Black Swan
Playing a prima ballerina proved a challenge for more ways than one for Natalie Portman, who shed 20 pounds for the role by way of portion control and a rigorous workout routine.

"I think it was just the physicality of it all that was the most extreme," she told US Magazine. "I mean, I had never gotten that much training - to be doing five-to-eight hours a day was really a challenge."

Still, it was probably worth it for the Oscar, eh?

Christian Bale for American Hustle
Having previously dropped a ton of weight for roles in The Machinist and The Fighter, Christian Bale finally got to eat all the pies for his part as paunchy con-artist Irving Rosenfeld in David O. Russell's American Hustle.

But despite having done it a few times, Bale has insisted that a physical transformation is all just part of the job. "Believe me, I don't go looking for these things," he told Access Hollywood in 2010. "If it does happen, it's like, 'Oh damn, I have to do that again, because I just tend to fall for the movie, the character, and then I'll realise, 'Oh man, I gotta do that.'"

Anne Hathaway for Les Miserables
A miserable diet of lettuce was the chosen method for Anne Hathaway, who lost nearly two stone to play Fantine in last year's hit musical, Les Miserables.

"I didn’t think I would be able to keep going without collapsing," she told Metro at the time. "But I had to appear dead.

"If you are not willing to cut off your hair, lose weight and look an idiot singing, the role is not speaking to you enough."

Tom Hanks for Cast Away
Double Oscar-winner Tom Hanks had bulked up for A League of Their Own and slimmed down to play AIDS patient Andrew Becket in Philadelphia, but his 50 pound weight loss for Cast Away saw the actor become skeletal.

This year, the actor revealed that we won't see his weight fluctuate for a part again after being diagnosed with Type 2 diabetes.

Speaking at the London Film Festival, he said: "I've talked to a number of actors who have gained weight for roles and just out of the sheer physical toll on one's knees and shoulders, no one wants to do it again. I think that's more or less a young man's game."