Actors are masters of disguise. They literally become other people. Most of the time they’re permitted to look mostly like themselves, the symmetrically featured, good looking humans, who others love to watch on film.

When actors take on roles that are a stretch for them, it’s a big challenge. Sometimes it means transforming the way they look or act in the process. These sacrifices for a role often lead to awards and critical acclaim, leading to other game changing parts. Some actors lead their lives like chameleons subscribing to method acting, literally becoming the person they portray on screen. Some abandon this practice as they age, as it’s too hard on their bodies, or they want to focus their time on their families, where others can’t get enough of who they can become next. Here are 20 stars who completely transformed the way they look for a role and how they did it.

20 Rami Malik Became Freddie Mercury

Rami Malik knew he had to fill larger than life platform shoes to become Freddie Mercury. To get a believable performance, not only did Malik have to wear a mouth prosthetic, he had to learn to both talk and sing with it in place. No wonder people can’t stop talking about Bohemian Rhapsody!

19 Gal Gadot Became Wonder Woman

Wonder Woman is an Amazon Warrior, not a lithe fashion model. When Gal Gadot took on the role of Wonder Woman producers wanted to make sure that Gadot looked like she could fight. So, they put the actor on orders to bulk up and put on a lot of muscle with the same trainers as other DC leading characters have used. Her program focused on eating protein, drinking water, working out for at least an hour each day, and getting enough sleep.

18 Charlize Theron Became A Monster

Becoming a 'Monster' for the 2003 film won Charlize Theron an Oscar. The star needed to put on weight, around 30 pounds, and wear dentures to hide her Hollywood pearly whites. In the editing side of things, they used translucent washes of tattoo ink to make Theron’s normally dewy skin look rough and weathered and added the effect of making the ends of her hair look damaged and uncared for.

17 Heath Ledger Became The Joker

Method acting was said to be the key to Heath Ledger’s terrifying and brilliant performance as the Joker in The Dark Knight. The star spent a month locked up in a hotel room and his apartment to master his part, and even journaled about it and clipped items like photos of hyenas and Alex from A Clockwork Orange as inspiration for Joker. Many people say that Ledger took the role too far and that it ultimately led to his isolation and his early death. Heath won a posthumous Oscar for the part.

16 Anne Hathaway Became Fantine

In order to portray the depths of despair her Les Misérables character Fantine was going through, Anne Hathaway had to give it her everything. In addition to lopping off her trademark long chestnut hair, her life on camera, and living off little more than kale and oatmeal for weeks before filming, she banished her husband because he was making her too happy. The star told Chelsea Handler on her show, “I love him so much that I was like, ‘You’re making me happy. You’re keeping me up and I’m clawing to the sides of my life and I need to fall into a pit and you need to go, honey.’”

15 Naomi Watts Became The Princess Of Wales

Being a princess is all about the hair. Just ask Disney! The transformation of Naomi Watts into everyone’s favourite princess was all about getting the 1980’s blonde tresses just right. Many actors say that once they have the makeup and hair just right it’s that much easier to become the person you’re portraying. It’s likely this is the case for Watts, whose portrayal of Lady Di was spot on.

14 Vincent Kartheiser Became An Aging Pete Campbell

Time was not kind to Pete Campbell, but it was to actor Vincent Kartheiser. This meant that the Mad Men crew needed to prematurely age the actor, which meant shaving and contouring his hair to look like he was balding and adding some girth to his aging belly by putting 25 pounds onto his regular frame. Kartheiser joked about shaving his hair saying, “Most of my friends were like, Dude, don’t do that, it might never come back in! But luckily I have a good head of hair.'

13 Rooney Mara Became The Girl With The Dragon Tattoo

When you change your look for a role that makes you a star, you might be able to remain anonymous even when your film becomes a big hit. In order to become Lisbeth Salander, Mara Rooney relied heavily on make-up artist Pat McGrath who coloured and chopped her long chestnut into a pitch-black shade with a severe haircut. Next they bleached her eyebrows and added piercings, tattoos, and a ton of make-up.

12 Chris Pratt Went From Average Guy To Superhero

You might be familiar with Chris Pratt’s “Where’s my next snack?” IG series where the star, who was under an intense workout and eating plan posted about how he was preparing for his new Superhero roles. The once average Joe who played the lovable Andy Dwyer on Parks and Recreation needed to transform into a muscle laden superhero for two roles which became a part of a larger franchise – Guardians of The Galaxy and Jurassic World. We see many more morning workouts in this star’s future.

11 Natalie Portman Became A Prima Ballerina

Ballerinas are known for being petite, and for their endless dedication to their craft. When Natalie Portman prepared for Black Swan, she threw herself into the ballerina life, living on what prima ballerinas eat, and practicing as much as 16 hours a day. In retrospect Portman says she ended up, “method acting without intending to.”

10 Demi Moore Became G.I. Jane

Demi Moore went from a teen star and member of the infamous Brat Pack to someone who wanted to prove her abilities as an adult actor. To do so she threw herself into the physicality of her roles. For her leading role in GI Jane she trained like she was really in the army and shaved off her brown hair.

9 Sean Aston Became A Hobbit

Sean Aston was dabbling in marathon running when he was cast to play the part of Sam in the Lord of The Rings trilogy. The thing is, Hobbits don’t run, they’re too busy eating their second breakfasts and elevensies. For 274 days during filming and the three years that followed, each with up to six weeks of pick-up shots, Aston needed to put his athletic pursuits on hold.

8 Cate Blanchett Became Bob Dylan

Cate Blanchett was a smash playing a young Bob Dylan. Thanks to the study of mannerisms of the folk singer along with just the right wardrobe, sunglasses, and wig, we almost believe we’re watching Dylan in I’m Not There. For this role it took six actors, including Blanchett to portray Dylan through various stages of his life.

7 Tom Cruise Wasn't Afraid To Drop The Heartthrob Status For Tropic Thunder

Tom Cruise generally plays conventionally attractive action heroes in his roles. When he was cast in the comedy Tropic Thunder it gave him a chance to have fun and get a little silly. For his cameo in this role Cruise wore a full body suit, a bald cap, and prosthetic hands, looking like a completely different person.

6 Renee Zellweger Became Judy

Renee Zellweger first dipped her toes into the water of transformation for a role when she became the very average Bridget Jones in the 1990s. She’s still not afraid to change her looks for the right part. Recently she chopped and dyed her blonde hair to become Judy Garland and tell the story of the last year of the legend’s life.

5 The Boys Of Riverdale Undergo Regular Dye Jobs

Casting agents think nothing of a person’s hair colour when casting roles. Thanks to computer technology they can easily see what someone will look like as a brunette or redhead, in the case of these two boys from Riverdale. Cole Sprouse who plays Jughead on Riverdale routinely needs to have his ash blonde hair darkened to a raven black, while KJ Apa who plays Archie needs to have his brown hair transformed into the iconic carrot top red Archie is known for.

4 Chris Hemsworth Became Thor

We’re so used to seeing a buff Chris Hemsworth in his role as Thor, and a slightly different out of shape version care of the recent Avenger’s End Game movie, that it’s easy to forget he was once a young no-name looking to get his start. With this being the role that launched him, Hemsworth had to dedicate himself to fitness. Hemsworth said about the hours working out, “alternate between heavy weightlifting, bodybuilding work to lighter timed fitness and more resistance and functional type stuff”.

3 JK Simmons Gets Pumped For Justice League

Getting fit for a role in Hollywood is normal. When you’re 61 it’s a little less likely, but that didn’t stop JK Simmons for his preparation to play Commissioner Gordon in the Justice League movie. His trainer Aaron Williamson took to IG to boast of Simmons’ commitment to the role saying, “Saturday morning, 61 years old & making the young generation jealous. This is what dedication looks like."

2 Zac Efron Gets A Beach Body

When Zac Efron knew he’d be standing next to Dwayne Johnson in the Baywatch movie and taking off his shirt frequently, he upped his work out routine. Even fitness experts complimented Efron on his physique which came thanks to leafy greens and free-range protein. Steve Weinberger, head judge for the National Physique Committee and the International Federation of Bodybuilding and Fitness says Efron’s build is fantastic for physique competitions, “who prefer to develop a less muscular, yet athletic and aesthetically pleasing physique.”

1 Emma Stone Goes Pro Tennis

Emma Stone needed to look like a pro athlete in order to be able to compete in Battle of the Sexes. This meant a lot of time at the gym so she would look like she could hit the ball like tennis legend Billie Jean King. The star gained 15 pounds of pure muscle. It was reported that her workout included, “walking with dumbbells, also known as heavy farmer's walks, and 300-pound hip thrusts. She could eventually deadlift up to 185 pounds and could do push-ups with 50 pounds of chains on her back.”

Sources: Business Insider, Time, Cosmopolitan, Vanity Fair, Hollywood