7 Tom Hanks, along with his costars, had to endure a period of severe training for Saving Private Ryan (1998). For 10 days they had to undergo weapon drills, close combat training, maneuvers, and the language and signals of WWII.

That wasn’t all they had to do. They were told to use their character names during that time. They had to train in terrible weather conditions, getting wet and freezing cold. They had hike five miles a day carrying 40 pounds of gear on their backs. The hardships brought them together as a team which helped them play their roles effectively. According to Tom Hanks, the exhaustion and longing for it to stop was exactly what the characters had to feel in the movie.(source)

8 For the movie Ray (2004), Jamie Foxx in addition to shedding 30 pounds had to wear prosthetic eyes over his eyes for 14 hours a day during the entire shoot.

The movie revolves around the life of rhythm and blues musician Ray Charles who lost his sight at the age of four due to glaucoma. Charles invited Jamie Foxx to play the keyboard, which Foxx managed to do well enough. It is said that Charles was trying to test him as a person rather than as a musician. He gave him some complicated pieces to play. Though Foxx couldn’t entirely succeed Charles was convinced that reportedly hugging himself in joy that he got what it takes to play the role.(source)

9 Bryan Cranston of Breaking Bad was actually taught how to cook meth by the DEA to prepare for his role.

Walter White is a chemistry teacher diagnosed with lung cancer who turns to manufacturing meth to provide for his family in the show and wonderfully played by Bryan Cranston. According to an interview he gave, they were taught the whole process to make the scenes look believable, though they never really cooked it for real. Cranston would also isolate himself from the rest of the cast and crew so that he could focus on the scene when the camera rolls.(source)

10 Vincent D’Onofrio holds the record for most weight gained, 70 pounds, for his role as a fat clumsy marine Pvt. Leonard Lawrence in the movie Full Metal Jacket (1987).

D’Onofrio sent his audition tapes, because a suggestion from his friend, to the director Stanley Kubrick. He received the role after three more tapes after which he gained the weight required for his role. Until then it was Robert De Niro who held the record for gaining 60 pounds for his role in the movie Raging Bull (1980). He also managed to lose the weight in nine months after the filming was complete with a diet of chicken nuggets and seeds to be ready for his next movie.(source)

11 To get the role of Jim Morrison, Val Kilmer learned 50 songs from Doors for the movie The Doors (1991). He sang so well that when the real Doors members heard the songs they couldn’t tell if it was Kilmer or Morrison.

That was not all he did. Val Kilmer spent thousands of his own money to make an eight minute music video of him singing and dressed up like Jim Morrison at various stages of life. Later when he got the job Paul Rothchild, record producer of The Doors, took him away and spent hundreds of hours telling him anecdotes, various moments, and the thinking of Jim Morrison. Kilmer also visited the studio where Rothchild gave suggestions about pronunciation and other idiomatic things that would make him sound like Morrison.(source)

12 Robert De Niro did whatever it took to get it right for his roles in any movie he was in. He gained 60 pounds for Raging Bull (1980) and learned to box for his role as Jake LaMotta.

There probably is a long list of things he had done to make sure he gave everything to the character he portrayed. He learned to play saxophone for the movie New York, New York, he lived in Sicily for The Godfather Part II, he gained weight yet again for The Untouchables, and even worked as a cab driver for weeks for Taxi Driver. He even threw anti-Semitic remarks at Jerry Lewis, during the filming of The King of Comedy, who got so angry that he forgot there were cameras and grabbed De Niro’s throat, which was exactly what was needed for the scene.(source)