In Hollywood, some thespians take their art so seriously that they don't hesitate to transform their body in order to play a role.

This can involve losing or gaining weight, undergoing hours of makeup application, and wearing tons of prosthetics. But it's a small price to pay for fame and fortune, right?

Below is a list of the most memorable transformations that have certainly made an impact on the big screen:

Ryan Reynolds gained 25 pounds of muscle for his role in "Blade: Trinity."

Natalie Portman lost 20 pounds to play a ballerina dancer in "Black Swan."

Christian Bale lost more than 63 lbs. for his role in "The Machinist," bulked up in "The Dark Knight" and piled on the pounds to play a chunky conman in "American Hustle".

Robert De Niro changed his body type twice to play the iconic boxer Jake LaMotta in "Raging Bull."

George Clooney ditched his clean-shaven appearance for an award-winning part in "Syriana."

Rooney Mara received several facial piercings and shaved her head to play "The Girl with the Drag

"30 Seconds to Mars" frontman and actor Jared Leto gained close to 70 pounds for "Chapter 27."

Charlize Theron gained 30 pounds for her Oscar-winning role in "Monster."

Tom Hanks spent a year losing weight for "Cast Away."

Cate Blanchett played legend Bob Dylan in "I'm Not There."

Do fat suits count? John Travolta donned such a suit and fake Baltimore accent to play a kooky lady in "Hairspray."

Hilary Swank spent weeks physically and mentally preparing for a transgendered role in "Boys Don't Cry."

Demi Moore shaved her head and gained muscle for "G.I. Jane"

Ben Kingsley shaved his head and lost 20 pounds to play Gandhi.

50 Cent lost around 50 pounds for "All Things Fall Apart."

Matt Damon gained more than a few pounds for his role in 2009's "The Informant!"

Cameron Diaz underwent a major hair change for "Being John Malkovich."

Dustin Hoffman played a woman in "Tootsie."

Gwyneth Paltrow wore a fat suit in "Shallow Hall."

Tom Cruise wore a fat suit and prosthetics to play Les Grossman in "Tropic Thunder."

Cruise wasn't the only one in "Tropic Thunder" to alter his appearance. Robert Downey Jr.'s wore blackface.

John Hurt wore prosthetics to channel a deformed Joseph Merrick in "The Elephant Man."

Daniel Day-Lewis put a year of preparation into his role of Abraham Lincoln.

Eddie Murphy wore a foam and prosthetic suit for "The Nutty Professor."

Renée Zellweger has both gained and lost weight for her film roles, especially in "Bridget Jones's Diary."

Rebecca Romijn was painted blue and wore hundreds of plastic scales in "X-Men", yet still ended up looking smoking hot.