Chris Pratt - Guardians of the Galaxy
Hollywood is no stranger to portraying extremely high body-type standards, but sometimes actors take this a little too far while filming for a specific role. Some of these body transformations even damaged the long-term health of some of these celebs. Check out this gallery, and see the most shocking physical transformations actors took on while filming various roles. 
Chris Pratt looks great, even with a dad bod.
However, with a perfect physic, which he developed for Guardians of the Galaxy, he looks the best he can possibly be. The film's producers hired him to play the lead role of 'Star-Lord' on one condition-- that he would turn that belly fat into rock-hard abs. From this transformation, it's pretty obvious he succeeded the best he possibly could.
Robert Downey Jr. - Iron Man
Robert Downey Jr. has worked on all types of movies, but he never had a very muscular being shown while filming for these roles.
When it came time to film the huge-budget film Iron Man, Downey had to make some changes to his diet and spend some time at the gym. It proved to work well because he looked more like Hulk than he did Iron Man with that body.
Christian Bale - The Machinist
Christian Bale is one of the best-known actors when it comes to body transformations. He has bulked up for roles in films such as The Dark Knight and American Psycho and has put on some major weight for his role in American Hustle.
But probably most notably, his craziest weight transformation came when he played the role of Trevor Reznik in The Machinist when he lost so much weight in such a short amount of time, it caused permanent damage to his body.
Bradley Cooper - American Sniper
Bradley Cooper was known as the fun-loving actor of Hollywood for the majority of his roles, but when it came time to bulk up for the film American Sniper, Cooper took it very seriously. He bulked up and looked like a completely different person.
In order to reach this military body type, he has a very strict gym regimen as well as a healthy diet. Along with American Sniper, Copper bulked up for the film Guardian Of The Galaxies as well for his role as Rocket Raccoon.
Chris Hemsworth - Thor
When Chris Hemsworth was cast as the god of thunder for the film Thor, he knew he had to pack on some serious muscles, especially as he was coming off filming the movie In the Heart of the Sea, a role for which he had to shed some serious pounds, which you can see from the side-by-side photo.
In preparation for the role of Thor, Hemsworth hit the gym with trainer and former Navy SEAL Duffy Gave, who helped Hemsworth pack some serious muscle, especially in his arms and shoulders.
Margot Robbie - Suicide Squad
There's no doubt that Margot Robbie is known for her stunning looks, but ever she had to intensively train for her role as Harley Quinn on the film Suicide Squad. The Australian bombshell geared up for the film very quickly, thanks in part to her trainer Andie Hecker, founder of Ballet Bodies. Hecker worked with the 26-year-old actress to define her abs by using the Pilates reformer and incorporating a lot of cardio as well.
Ryan Reynolds - Blade Trinity
Ryan Reynolds may be the stereotypical nice guy in Hollywood, but his muscular performance in Blade Trinity was due to many hours spent in the gym. Back in the early 2000's, Reynold was cast playing small parts in cheap comedies, even donning a fat suit for his performance in Just Friends.
But in 2004, Reynolds got his big action movie break starring in the third installment of the Blade movies, playing the Hannibal King. After the film, Reynolds kept his body in shape, a decision the proved to be right when he starred in the film X-Men Origins: Wolverine and eventually Deadpool.
Chris Evans - Captain America
Evans went from college-boy body to chiseled specimen to bring his character to life in the film Captain America.In order to fit the part, Chris had to spend months at the gym, and keep watch on everything he eats.The final result looked spectacular, and Evans looked identical to his buffed comic book counterpart.
Additionally, Evans signed a contract for him to play the role of Captain America in another 10 movies, which means he has to maintain his physique for the entire time!
Gal Gadot - Wonder Woman
This Israeli beauty queen served two years in the Israeli Defense Forces and even studied law and international relations, all before she became a Hollywood Actor. When she was in the running for Miss Israel and then eventually Miss Universe, Gadot slimmed down to the thinnest she had ever been.
However, when she was cast as Wonder Woman, she knew it was time to bulk up and hit the gym and ran at least two miles a day.
Aaron Taylor-Johnson - Avengers: Age Of Ultron
Aaron Taylor-Johnson’s transformation from scrawny teen to big-hunk Quicksilver took quite the commitment. When approached to take on the role in the film, Taylor-Johnson was concerned about the body transformation he had to go through.
Although he played in some major action movies before, including a hero in the film Kick-Ass, he needed to buff up to fit the role of Quicksilver. In order to begin the intense gym schedule that focused on his arms, chest and legs.
Paul Rudd - Ant-Man
When Paul Rudd got the call to play Ant-Man, the first thing he did was head to the gym. The 40-year-old took his superhero transformation seriously, and completely transformed his body for the better.
This shows that even the most fun-loving guys of Hollywood can transform into a superhero hunk.
Charlie Cox - Daredevil
In Netflix’s original Daredevil, Charlie Cox not only has to consistently look good for the camera, but he has to pretend he can’t see anything in front of him. Because filming for television takes longer than filming movies, Cox had to keep up his cut figure.
He had to completely transform his lifestyle so he can stay in shape and shoot those fight scenes for a continuous 9 months.
Thomas Haden-Church - Spiderman 3
Challenging for Thomas Haden-Church, his performance as Sandman in the film Spider-Man 3 about both bulking up and working side-by-side with CGI.
Producers offered to use special effects to bulk him up, but he preferred the old-fashion way of hitting the gym and getting muscles the natural way.
Hugh Jackman - X-Men
When Hugh Jackman signed on to play the role of Wolverine in 2000's 'X-Men' movie, he had no idea he signed a multi-decade contract with the gym as well.
For every 'X-Men' movie, Jackman had to spend at least six months at the gym, making his muscles look like a greek god and making sure his diet isn't hurting his body.
Don Cheadle - Iron Man 2
Don Cheadle is one of the most well-known actors in Hollywood, but he's not very well-known for the role of James Rhodes body in Iron Man 2. Once Terrence Howard left the franchise after the initial Iron Man movie, Cheadle took the part of Rhodes and got into shape in such a short amount of time.
Cheadle's performance was so good that he was invited to perform in the 3rd Iron-Man movie, and became an Avenger in the film Avengers: Age of Ultron.
Andy Serkis - Lord Of The Rings
Actor Andy Serkis is no stranger to insane physical transformations, especially after his role as Gollum in the Lord of the Rings movies.
Also, when it came time to play the character Klaw in Avengers: Age of Ultron, it was no different when it came to a physical transformation.
Andrew Garfield - The Amazing Spider-Man
Andrew Garfield had a pretty hard time transforming his body to that of the teen superhero Peter Parker, also known as Spider-Man. Garfield had to work out strenuously every day and keep a strict diet, which apparently made him miserable, but at least he achieved the ideal body of Spider-Man.
In order to achieve that body type, Garfield had to abandon all junk food and sweet drinks from his diet, and he had to eat meals that were specifically made for him.
Karen Gillan - Guardians of the Galaxy
When Karen Gillian got the role of Nebula on 'Guardians of the Galaxy', she had to bulk up and get some muscles. In order to prepare for the role, she continually went to the gym. When it came to preparing for the role, Gillan said, “I trained with a personal trainer four times a week to bulk up.
I don’t work out as much normally so it was pretty intense. And then every day I wasn’t working on the film I’d have to do martial arts and they’d teach me how to kick and punch over and over again. It felt like I was in a Rocky montage.”