▲Exploring both the internal and external aspects of a role, De Niro could become the character on-set and off-set, which has led to some incredible stories and performances.

▲In 1980, De Niro had one of his biggest performances in 'Raging Bull.' He reportedly put on 60 lb (27 kg) and learned how to box for the role.

▲De Niro was playing Jake Lamotta, and actually trained with the famous boxer, who apparently said De Niro had what it took to be a real contender.

▲De Niro studied with Hollywood legend Stella Adler, who taught him the all-important Stanislavski system.

▲To build a brotherhood, De Niro and Joe Pesci lived and trained with each other. Since then, the two have remained friends and frequent collaborators.

▲He was back to method acting in '90s thriller 'Cape Fear.' He worked out for several months and during filming, and reportedly lowered his body fat to just 3%.

▲The actor went through extensive training, and even entered three Brooklyn boxing matches. With two wins, he hasn't got a bad record.

▲Robert De Niro apparently paid a dentist a large sum to make his teeth look bad. After filming wrapped up, De Niro paid him yet again to fix them.

▲His character, Cady, has one creepy southern accent. De Niro apparently taped locals from southern states reading out the script, and mimicked it. It's said that he even rang up Scorsese and left voicemails in the creepy voice.

▲He also studied the effects of mental illness, and visited an American Army base in Northern Italy, where he taped conversations with Midwestern soldiers.

▲'Taxi Driver' helped solidify De Niro as a near-perfect on-screen presence. He famously spent around 15 hours every day driving cars and preparing for the role.

▲De Niro's turn in 'The Godfather Part II' is one for the history books. Playing a young Vito Corleone, the actor spent three months in Sicily to prepare for the role.

▲The Stanislavski system (pioneered by Konstantin Stanislavski) is what's known as the "art of experiencing," and is basically an academic term for method acting.

▲Co-star Jodie Foster once claimed that De Niro would repeatedly ring her and ask for a coffee date. They reportedly rehearsed their dinner scene over and over, with De Niro refusing to give up.

▲The actor tracked down Capone's tailors, and asked for identical clothing for his wardrobe. He even insisted on having the same silk underwear, despite the fact you can't see them in the film.

▲De Niro didn't have long before they started filming 'The Untouchables.' Although he gained weight to play Al Capone, he also wore pads and pillows to bulk up.

▲De Niro was a shining star in Elia Kazan's final film, 'The Last Tycoon.' The actor apparently cut his weight down from 170 pounds (77 kg) to 128 pounds (58 kg) to play the role of Monroe Stahr.

▲In 1977, the actor learned to play the saxophone to portray a sax player in 'New York, New York.' We expect nothing less.

▲Elia Kazan wasn't quiet when singing De Niro's praises. "[He] is one of a select number of actors I've directed who work hard at their trade, and the only one who asked to rehearse on Sundays. Most of the others play tennis."

▲De Niro was on fire in 'The King of Comedy.' In one scene, he used anti-Semitic slurs against co-star Lewis, to provoke him into a memorable performance.

▲Tensions were high on the set of 'The Deer Hunter,' and the tables were turned on De Niro. During filming, Christopher Walken was persuaded to spit on De Niro, who apparently nearly walked off set in rage.

▲The characters play Russian Roulette in one scene, taking turns slapping each other. The slaps were real, as was the palpable anger on the actor's faces.

▲It paid off. Lewis apparently had little experience with method actors, and said "I forgot the cameras were there... I was going for Bobby's throat."

▲In another scene, Robert De Niro requested a real gun to play Russian Roulette. This helped build more tension, but the chamber was checked in between every take.

▲For 'Heat,' De Niro deliberately didn't rehearse a scene with Al Pacino, playing up the unfamiliarity between the two characters.

▲In the mid-'80s, De Niro reportedly grew weary of being typecast as a mobster. He starred in different films like surreal 'Brazil' and rom-com 'Falling In Love.'

▲In the latter, the actor went to great lengths for authenticity. He even had business cards made for his character.

▲Robert De Niro and Richard Romanus clashed during the filming of 'Mean Streets.' This added to their on-screen rivalry, and leads up to an important climactic scene, which won't be spoiled here.

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De Niro's endless commitment followed through into his directing. He couldn't play a part in 'The Departed' due to directing 'The Good Shepherd.' "I wish I could've been able to," he said.

De Niro also features in this list of great actor-director duos.

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The actor has Italian roots, but he spent around four months learning the Sicilian dialect. Nearly every line he speaks is Sicilian. Of course, the hard work paid off.

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Robert De Niro will be remembered as one of the greatest actors ever. The American star has already proved himself over the course of nearly eight decades, and he's not slowing down either, still churning out big performances in his late seventies.

It's high time you revisit what makes De Niro so incredible: his elaborate methods. The actor has been a pain on set for years, requesting silk underwear, bossing directors around, and using real bullets for Russian Roulette. Click on to revisit the craziest stories of De Niro's iconic career, and find out what makes his performances so pitch perfect.