Being a Hollywood film star sounds like an amazing job for most people. After all, these actors are being paid millions of dollars, traveling all over the world, having fun, and mixing with other celebrities. There are plenty of perks and they get to be famous - what could be better?

On the surface, being an actor seems like a great job, and it is, but that doesn't mean a little hard work isn't required every now and again.

Sometimes actors even choose to go to extremes for their art. This can include transforming their bodies, undergoing strenuous training, wearing make-up or uncomfortable prosthetics, and in extreme cases isolating themselves so that they can fully immerse into their character.

Today we're looking at 20 actors who took their roles seriously, maybe even a little too seriously. Some of them were well-rewarded for their efforts while others didn't fare as well...

20 Christian Bale Wasted Away For His Role In The Machinist

Christian Bale is well-known for his ability to transform his body for a role. He famously wasted away in just a matter of months for his role in The Machinist, only to bulk up again to play Batman. More recently, he gained a whopping 50 pounds to portray former U.S. Vice President Dick Cheney in Vice. Couldn't he just have worn a fat suit?

19 Val Kilmer Was Obsessed With His Character In The Doors

Val Kilmer became so obsessed with playing Jim Morrison in the 1991 film, The Doors, that he needed therapy to detach himself afterward. He spent hundreds of hours learning 50 of Morrison's songs and constantly questioned people who had known the singer in real life. He even insisted that everyone on the set call him "Jim".

18 Heath Ledger Isolated Himself To Prepare For His Joker Role

Heath Ledger wanted to make sure that his Joker character was the best it could be so he isolated himself for weeks to perfect his performance. “I sat around in a hotel room in London for about a month, locked myself away, formed a little diary and experimented with voices— it was important to try to find a somewhat iconic voice and laugh," he said.

17 Anne Hathaway Made Herself Miserable To Perform In Les Miserables

To truly understand the desperately poor character she plays in Les Miserables, Anne Hathaway went to great lengths to make herself, well, miserable. She went without food and isolated herself to really get a sense of the deprivation her character would be feeling. She might have got a bit too far but it made for a brilliant performance.

16 Viggo Mortensen Spent A Year Preparing For A Role He Didn't Get

When Viggo Mortensen was cast in Oliver Stone's Platoon, he thought the film would be his big break. He spent a full year preparing to play Sgt Elias, learning everything he could about the Vietnam War. But just before filming began, the director decided to hire a better-known actor for the role and replaced Viggo with Willem Dafoe. Ouch.

15 Leonardo DiCaprio Suffered Freezing Conditions To Film The Revenant

When asked if there were any moments when he regretted taking on the role of Hugh Glass in The Revenant, this is what Leonardo DiCaprio had to say: "I can name 30 or 40 sequences that were some of the most difficult things I’ve ever had to do. Whether it’s going in and out of frozen rivers, or sleeping in animal carcasses, or what I ate on set. I was enduring freezing cold and possible hypothermia constantly."

14 Shia LaBeouf Decided To Pull Out A Tooth For His Role In Fury

We're not sure who Shia LaBeouf was trying to impress when he pulled out one of his teeth and slashed his face to prepare for his role in Fury, but we don't think it worked. His method-acting technique also included not bathing for two weeks before filming began. Really, Shia?

13 Margot Robbie Transformed Her Face With Prosthetics For I, Tonya

Margot Robbie went all out to play a disgraced figure skater in the 2017 biopic I, Tonya. She spent months learning to ice-skate and even suffered a herniated disk in her neck during this intense training. She also wore uncomfortable prosthetics and retro 80's wigs to make her look just like her character.

12 Daniel Day-Lewis Broke Ribs Playing His Character In My Left Foot

Daniel Day-Lewis won his first Oscar in 1989 for his outstanding performance in My Left Foot. In the movie, he played Christy Brown, an Irish writer and painter who was born with cerebral palsy and was able only to control his left foot. Throughout the filming, the dedicated actor remained slumped over, eventually causing two of his ribs to break. Wow - talk about dedication!

11 Jamie Foxx Wore Blinding Prosthetic Eyelids To Play Ray Charles

When Jamie Foxx played Ray Charles in the 2004 biopic Ray, he went all out to transform himself into his character. Not only did he lose weight, but he also chose to wear prosthetic eyelids to accurately mimic the movements of a blind man. But it was hard work and Jamie suffered from frequent panic attacks during the first few weeks of filming.

10 Robert De Niro Worked As A Cabbie To Prepare For Taxi Driver

The reason that Robert De Niro was so convincing in his role as a cabbie in Taxi Driver was because he actually drove a cab to prepare for the movie. He got himself a cab driver’s license and reportedly worked for a month to help him better understand his character. It paid off - his performance earned him an Oscar nomination.

9 Adrien Brody Gave Up Everything For His Oscar-Winning Role

Adrien Brody quite literally gave up everything for his Oscar-winning role in The Pianist. “I gave up my apartment, I sold my car, I disconnected the phones, and I left,” he said. “I took two bags and my keyboard and moved to Europe.” He also lost close to 30 pounds and practiced playing the piano for four hours a day.

8 Natalie Portman Endured Gruelling Ballerina Training For Black Swan

To prepare for her role as the overly ambitious Nina in Black Swan, Natalie Portman went to dangerous extremes. She became waif-like on a diet of just carrots and almonds and spent up to eight hours a day learning ballet and rehearsing. "There were some nights that I thought I literally was going to die," she said.

7 Charlize Theron Shaved Her Eyebrows And Fried Her Hair For Monster

To complete her transformation from classic Hollywood beauty to the dangerous Aileen Wuornos, Charlize Theron wore dentures to hide her pearly whites and had her beautiful blonde locks thinned out and fried repeatedly. She also shaved her eyebrows and wore thick makeup to conceal her flawless skin. No wonder she looked almost unrecognizable!

6 Rooney Mara Got All Her Character’s Piercings

Rooney Mara went all out to play Lisbeth in The Girl With the Dragon Tattoo. She cut off her long blonde locks, dyed her hair black, and bleached her eyebrows. She also decided to get all of her character's piercings as she felt as though these were a crucial part of the costume. The result? An actress we barely recognized.

5 Halle Berry Didn't Bathe While Filming Jungle Fever

For her first-ever film role, Halle Berry played the role of a street woman in Jungle Fever. She decided to go for character authenticity so for the whole ten days of shooting she didn't bathe. "It’s true (I didn’t wash), ask Sam Jackson, he had to get a whiff of it!” she revealed in an interview.

4 Mia Farrow Ate Raw Liver For Rosemary's Baby

Director Roman Polanski was obsessed with getting every detail right in his 1968 horror film Rosemary's Baby. He even coerced actress Mia Farrow into eating genuine raw liver, something she revealed in her autobiography. “When Roman wanted me to eat raw liver, I ate it, take after take, even though, at the time, I was a committed vegetarian,” she wrote.

3 Nicolas Cage Had An Elaborate Costume To Play An All-CGI Character

After finding out that his character would be almost completely CGI in Ghost Rider, he suggested to the director that he wear voodoo face paint on the set. "I said to him 'Well look, if I do this can I wear a mask?' Because I was concerned about feeling ridiculous on the set," he explained in an interview. Maybe there's a method to his madness but we can't see it.

2 Robert Pattinson Slept In His Clothes For Two Months

To prepare for his role in Good Time, Robert Pattinson rented a cramped basement apartment and got a job at a car wash. He then took on the miserable life of the character he was going to play. "I never opened my curtains, didn’t change the sheets the entire time I was there, for those two months, and I would just sleep in my clothes,” he said.

1 Demi Moore Underwent Exhausting Navy SEAL Training

After Demi Moore landed the lead role in G.I Jane, she jumped at the opportunity to undergo simulated Navy SEAL training, to help her understand her character better. Not only did she participate in this exhausting training but the actress also shaved her head for the role. Way to go, Demi!