Whenever an actor gets cast in a movie, they're expected to put in 110%. Not only does their acting have to give a convincing performance, but they also need to look the part too.

Even though some stars get to maintain their dashing good looks, others must undergo a full, physical transformation - and they're definitely not glamorous.

Luckily, plenty of celebrities take these changes in stride, and boy does it ever pay off. Take a look at these 11 transformations and see if you can recognize these actors while in character!

1. Christian Bale in American Hustle

Most people are familiar with Christian Bale's muscular frame in movies such as American Psycho and the Dark Knight trilogy, fans were stunned to see how much weight the actor gained for American Hustle.

Not only did he have to perfect the comb-over, but he gained 43 pounds to play Irving Rosenfeld.

"It's easy to start with ... you're just sitting on your butt and you're eating lots of doughnuts and eating bread and everything like that," he told OTRC.com.  

"But you do it for two months and your body starts to rebel against you, it's just saying, 'No, please,' and your back is aching and there's also some problems with that," he added. "And then you've got to lose the weight at the end of it, you know? I wish it was simple."

2. Matthew McConaughey in Gold

To play the role of Kenny Wells in the movie, Gold, Matthew McConaughey had to do more than just gain a couple of pounds.

Not only did McConaughey have to add 47 pounds to his athletic physique, but he also shaved his hair in exchange of wearing a toupee, and had to wear fake teeth to cover his perfect smile.

While he's lost weight for movie roles, this was the first time he ever had to gain weight.

"I haven't ever done that. I said, 'McConaughey, you have six months to say yes to whatever you want to eat and whatever you want to drink. Whenever.' That was fun," he told E! Online. "The only thing that gets tiring is the thought of quitting. It was fortunate that I was like, 'Oh, this is also my job, so let's go"”all green lights.'"

3. Emma Thompson in Nanny McPhee

Typically known for her beauty and bright smile, Emma Thompson got a severe make-under when she played the part of Nanny McPhee in the self-titled children's movie.

It took an hour for the Oscar-winning actress to transform into character, which involved wearing a prosthetic nose, an unruly wig, fake warts, and a terribly large snaggletooth.

4. Warwick Davis in the Harry Potter series

Not only did Warwick Davis play Charms Professor Filius Flitwick and Griphook the Gringotts Goblin in the Harry Potter franchise, but he had to undergo a significant transformation for each role.

Each character required different physical alterations, which included prosthetics, contact lenses, and sharp false teeth.

"... the makeups feel very different when I wear them... the Griphook's much heavier. He's got bigger ears and nose.  And they're made of silicon, so silicon's a quite dense product," Warwick said in an interview Collider, adding he prefers Flitwick's less aggravating look.

5. Elizabeth Banks in The Hunger Games

When Elizabeth Banks was offered the role of Effie Trinket in the massively popular Hunger Games series, she knew her appearance would drastically change.

The actress's new look consisted of pink wigs, a powdered white face (sans eyebrows), and long jewel-encrusted nails, which she said made doing everyday tasks exceptionally hard.

"The nails [were] the worst part. I had these huge bejeweled nails. You can't undo a button," she said on The Ellen DeGeneres Show. "They are really cool. Completely impractical! I don't understand how anyone can use those."

"I couldn't use my Blackberry," she continued. "The biggest problem was I couldn't go to the bathroom. I had like, ladies in waiting... and I would stop drinking water. I felt so bad about bringing people to the bathroom with me."

6. Jared Leto in Dallas Buyers Club

A significant difference between Jared Leto and the rest of the actors on this list is that the Thirty Seconds To Mars frontman played a character of the opposite gender.

In Dallas Buyers Club, Leto played Rayon, HIV-positive transgender woman who helps sell the unapproved pharmaceutical drugs in Texas. Not only did the actor lose 40 pounds for a slimmer physique, he also shaved off his eyebrows, wore a face full of makeup, and waxed his entire body.

"I lost around 40 pounds and then I stopped counting. For me, it was about how it made me feel, how it made other people treat me," Leto said in an interview with The Guardian.

"I got down to something like 114 pounds, and that was enough to do what I wanted it to do, which was to change everything about me," the actor added.

Bonus fact: To get into the mindset of Rayon, Leto never broke out of character, even when he wasn't filming.

7. Nicole Kidman in The Hours

When Nicole Kidman played the real-life Virginia Woolf in the film, The Hours, many people weren't fond of her prosthetic nose, which not only completely changed her entire appearance, but made it incredibly distracting.

"What really put me off was The Nose,'' Martha Musgrove, a lecturer and doctoral candidate at the University of Ottawa, wrote on a Virginia Woolf e-mail exchange.

''Nicole Kidman wore a permanent frown and looked cross-eyed throughout the film, clearly distressed at this Thing in the middle of her face. Were Woolf's contemporaries preoccupied with her nose?" Musgrove continued.

It never really occurred to me that her proboscis was the defining feature, so to speak, of Woolf's appearance,'' she concluded.

8. Chris Hemsworth in In the Heart of the Sea

While we know Chris Hemsworth would survive if he was lost at sea, we know his buff bod would not.

For his role in the movie In Heart of The Sea, Hemsworth said in order to look like a starving castaway he was put on a diet of only 500 calories a day.

"We kind of went insane, weighing ourselves every day," Hemsworth told EW. "We all felt like a bunch of supermodels, trying to get down in weight for a show, or something. That's all we spoke about.

"You've got 15 burly blokes on the sea and all we talked about was our diet, and who'd lost more weight, and who's looking really skinny. It's ridiculous!" the actor added.

Along with his thinning physique, Hemsworth is sporting a shaggy hairdo, an unruly beard, and a fake sunburn to achieve his desperate-looking appearance.

9. Rooney Mara in The Girl with the Dragon Tattoo

When Rooney Mara was cast as Lisbeth Salander in the critically acclaimed film, The Girl with the Dragon Tattoo, she had to dramatically change her appearance.

Mara bleached her eyebrows, wore several piercings, shaved off half her hair, and dyed the rest of it black.

"The eyebrows were the biggest shock because that really changed my face, and I didn't recognize myself," Mara told Vogue. "But I was fine because I knew it was going to be really helpful for getting into character."

Makeup artist Pat McGrath played a hand in creating Mara's iconic look, and said it took several tries to perfect it.

"We went from the white-powdered sick-clown makeup to stitches in the face all the way to greasy, bloody eyes," McGrath explained. "I instantly knew how I could make her character so different. And then once the hair was cut in that mad shape, I was like, Well, the eyebrows have got to go. And in the end, it would look now and it would look new."

10. Jim Carrey in How The Grinch Stole Christmas

One of the most beloved Christmas classics, Jim Carrey became unrecognizable when he starred as the Grinch. While he won awards for his performance, he almost quit the role due to the difficulty of transforming into the character on set - which took two-and-a-half hours every day.

"It was like being buried alive each day. On the first day I went back to my trailer, put my leg through the wall and told [director] Ron Howard I couldn't do the movie," Carrey said during an appearance on the Graham Norton Show.

Luckily the crew came up with an unconventional plan to help him through it: "So a guy that trained CIA operatives how to endure torture was brought in. That's how I got through it," Carrey added.

11. Sean Penn in Carlito's Way

By now we're all familiar with Sean Penn's handsome facial features, but when he starred as sleazy lawyer David Kleinfeld in Carlito's Way, you wouldn't have been able to pick him out of a crowd. Not only had the actor dyed his hair brown and had it permed, he also decided to shave some of his locks off so it would look like his character had a receding hairline. Talk about dedication.

However, an American lawyer, Alan Dershowitz, believed Penn tried to copy his look, and even threatened to sue the filmmakers.

Want to see other major celebrity transformations? Take a look at these drastic changes:

• 10 Celebrities Who Transformed Themselves To Play Real People
• 11 Celebrities Who Proved It's Never Too Late To Get The Body You Want
• 15 Actors You Would never Recognize On The Street

[H/T: Brit+Co, TomorroWoman]