The Mindy Project alum had to gain 40 lbs. for his role in Live by Night.
This dramatic weight loss was one of many reasons the Les Misérables star took home an Oscar.
The Parks & Recreation star transformed into a fit superhero for Guardians of the Galaxy and never looked back.
The Spider-Man alum shocked fans when he debuted his bulging biceps, which are probably meant for his role in Justice League.
"I'd say my mother was worried," he admitted to E! News after losing 30 pounds for Nightcrawler. "I would say she just wanted me to be careful. But she also knew and knows how seriously I take what I do and she respects that."
The Friday Night Lights alum gained nearly 30 pounds of muscle to transform into a rookie-turned-professional boxer in Creed.
The 30 Seconds to Mars musician nabbed an Oscar for his riveting role in Dallas Buyers Club, but it cost him 40 pounds.
The Thor star went from muscle maniac to scary skinny for his role in The Heart of the Sea. After filming wrapped, Hemsworth returned to his muscular self.
The Spectacular Now star bulked up for his roles in Whiplash and The Divergent Series: Insurgent.
The Bridget Jones's Diary actress had to gain 30 pounds, not once, but twice for the lovable franchise's first and second films.
The actor shed 25 pounds for his role as a heroin addict in Other People's Children.
An actor hasn't startled us this much since Christian Bale whittled away to skin and bones in The Machinist. The Magic Mike hunk dropped 30 pounds to star in The Dallas Buyer's Club, the real-life story about a man dying from AIDS in the 1980s who treated himself with alternative remedies he smuggled into the United States from Mexico.
The actor lost 40 pounds to become shockingly ripped to play a killer opposite Tyler Perry in Alex Cross. He trained for five months with the same man who helps Daniel Craig get into James Bond shape.
The singer posted a picture of his newly beefed up bod on Twitter, writing, "I've been at Johnny Wright's compound working on my mind, music, and body for a new album release!"
The teen heartthrob went from cute kid to beefy babe as werewolf Jacob Black in the Twilight sequel. "The day I finished Twilight, I came home and started bulking up," Lautner told Interview magazine. "For New Moon, I'm 30 pounds heavier than I was in Twilight."
The actor lost a significant amount of weight for his role opposite Cameron Diaz in Sex Tape. "This time when I take my shirt off, I've made a promise to myself, it doesn't have to be funny," he told Us Weekly.
The up-and-comer has been spotted around town looking leaner for her starring role in The Girl With the Dragon Tattoo. According to a source, the actress is also cutting her hair supershort and doing Pilates workouts to achieve her character's "anorexic" look.
The actor is no stranger to morphing for movie roles. In 2004, he lost more than 60 pounds for his skeletal role in The Machinist, and he did it again for the upcoming The Fighter opposite a very bulked-up Mark Wahlberg. He also gained 40 pounds for both American Hustle and Vice, and lost 70 pounds for Ford v Ferrari.
The actor looked more like a god than a prince for his role in 2010's Prince of Persia. Gyllenhaal said he studied Parkour, the French art of street running, to bulk up for the film.
"All it is is time and discipline," the Oscar winner told Time magazine of his role in 2000's Cast Away, for which he lost over 50 pounds to play a man stranded on an uninhabited island.
The usually ripped rapper shocked everyone with this pic of him looking dangerously skinny. He reportedly went from 214 to 160 pounds in just nine weeks to play a football player diagnosed with cancer in Things Fall Apart.
No joke, but that's Carrot Top! Forget carrots, his biceps look like friggin' watermelons.
Shaping up for movie roles is nothing new. The legendary actor earned an Oscar nom for his role as terrifying tattooed rapist Max Cady in the 1991 thriller Cape Fear.
In order to portray former Vice President Dick Cheney, the star sported a fuller figure ahead of his performance in the biopic Backseat.