In Clint Eastwood's J Edgar, which opened in the US last week and will be shown here after Christmas, Leonardo DiCaprio achieves a remarkable transformation to play legendary FBI chief J Edgar Hoover.
DiCaprio is one of the most handsome men in the world, who dates supermodels and is an adored pin-up. But, in Eastwood's film he twists his finely chiselled features into suitably bitter contortions as the paranoid and vindictive Hoover.
He spends much of the movie wearing prosthetic liver spots, a bald wig and fake love handles. He even sports a dress at one point, and tries to kiss a reluctant male colleague.
DiCaprio could easily have rested on his laurels, but is one of those actors who insists on pushing himself. In recent years he's a played an abusive husband in Revolutionary Road, the unhinged billionaire Howard Hughes in The Aviator, and a deluded mental patient in Shutter Island.
Those last two films were made by Martin Scorsese, who has compared DiCaprio with Robert De Niro in terms of his commitment and lack of vanity. Most movie stars play versions of themselves in every film, but actors like DiCaprio, De Niro and a select band of others have the talent and the nerve to take on roles that push them to the very limit.
Here are some of those actors, and their career-defining performances.
Lon Chaney - Phantom of the Opera
In real life Lon Chaney Sr was a handsome, debonair actor who started out as a leading man. But he was also a master of make-up and disguise and at the height of his fame was known as "the man of a thousand faces".
His most astonishing transformation of all came in the 1925 silent film, The Phantom of the Opera, an ambitious drama based on the French novel by Gaston Leroux.
Chaney played the phantom and did his own make-up to create an unforgettably monstrous character.
He painted his eye sockets black to make his face more skull-like, used invisible wire to pin his nose back and distort his face, and wore a double-set of jagged false teeth. The end result was remarkable, and audiences are said to have screamed and even fainted when the Phantom's mask was first ripped away.
Anthony Perkins - Psycho
In the early part of his career, a fresh-faced Anthony Perkins was touted as the next James Dean, but his decision to play the lead in a 1960 Alfred Hitchcock film would change public perceptions of him forever.
The idea for Psycho was considered so tasteless and beyond the pale by Universal Studios that they refused to back it. So Hitchcock financed it himself, and cast Perkins as Norman Bates, the seemingly mild-mannered owner of a rundown highway motel.
Bates is actually a disturbed serial killer who holds conversations with his mother's desiccated corpse. Perkins almost made you sympathise with old Norman, and was so good in the role that he became somewhat typecast.
It was a surprising choice: only three years earlier Taylor had starred in Cleopatra, and now she was being asked to play a frumpy, drunken 50-ish university housewife.
With a remarkable lack of vanity, she gained 30 pounds, dyed streaks of grey into her hair and let herself go in a film full of explosive and unflattering scenes.
She and real-life husband Richard Burton were unforgettable as a middle-aged couple who air their dirty laundry during a drunken night in the company of a younger couple, and Who's Afraid of Virginia Woolf proved beyond a doubt that Taylor was an actress to be reckoned with.
Marlon Brando - The Godfather
By the early 1970s Marlon Brando's career had slowed to a standstill and he was renowned for being notoriously difficult to work with. So when Francis Ford Coppola was hired by Paramount to direct The Godfather and suggested Brando for the pivotal role of Mafia boss Vito Corleone, he faced stiff opposition.
The studio wanted Ernest Borgnine or Laurence Olivier, and couldn't imagine Brando in the role. So Coppola persuaded Marlon to do a screen test. The actor pinned his blonde hair back, stuffed cotton wool in his cheeks and transformed himself before Coppola's eyes into an ageing, wily crime boss.
When shown the test some studio chiefs didn't even recognise him, and one said "what are we watching -- who is this old guinea?" Brando was cast, won an Oscar and revived his career.
Robert De Niro - Raging Bull
One could have chosen any number of De Niro films, Taxi Driver for instance, but the actor's portrayal of 1940s middleweight boxer Jake LaMotta is perhaps his most impressive and complete transformation.
It was De Niro who persuaded Scorsese to direct the story of the self-destructive boxer's life, and got the real LaMotta on board as an adviser and boxing coach. De Niro learned to box and fought a couple of competitive bouts in preparation.
After all the fight scenes had been shot, he flew to Europe and spent four months on an eating binge in Italy and France, during which he ballooned from 145 to 215 pounds in order to play the older LaMotta.
The finished performance was remarkable in its intensity, and won De Niro Best Actor at the 53rd Academy Awards.
Meryl Streep - Sophie's Choice
Meryl Streep's chameleon-like qualities are well known, and early next year we'll see her deliver an extraordinarily accurate portrayal of Margaret Thatcher in The Iron Lady. But her most impressive early transformation was in Alan J Pakula's Sophie's Choice, where she played a young Polish woman in 1940s Brooklyn who's haunted by events in her recent past.
Based on a novel by William Styron, the film starred Streep as Sophie Zawistowski, a beautiful and hedonistic woman who tries, but cannot quite succeed, to immerse herself in a passionate affair with an unbalanced young man called Nathan.
Later we discover that Sophie is a Jew, and has been broken by an incident during the war when the Germans made her choose which of her two children would die.
Streep's rawness in the role of Sophie was truly memorable.
Daniel Day Lewis - My Left Foot
In agreeing to star in Jim Sheridan's My Left Foot, Daniel Day-Lewis set himself the ultimate challenge of playing Christy Brown, the Dublin author and painter who suffered all his life from severe cerebral palsy.
Throughout the shoot Day-Lewis stayed in character, and sat hunched in a wheelchair and was fed by other cast members. He broke several ribs during filming as a result of these contortions, and the story goes that when his agent turned up from England to see him, Day-Lewis refused to come out of character during the meeting.
On top of all the role's physical demands, Day-Lewis also had to master the intricacies of the Dublin accent, something very few foreign actors have managed. Needless to say, his was perfect, and the performance earned him his first Oscar.
Charlize Theron - Monster
On the face of it, Charlize Theron seemed an odd choice to play Aileen Wournos, a lesbian prostitute who bumped off six of her male clients in the late 1980s and early 1990s.
Ms Wournos had been unkempt and overweight: Ms. Theron was a former fashion model with little experience in serious dramas. But Theron more than rose to the occasion, gaining 30 pounds and using prosthetic teeth to make herself all but unrecognisable.
She was a revelation as Wournos, a seemingly monstrous serial killer whose tragic past was revealed in a series of flashbacks. American critic Roger Ebert called it "one of the greatest performances in the history of cinema", and the Academy judges agreed. Theron won Best Actress Oscar in 2003.
Heath Ledger - The Dark Knight
When Heath Ledger signed on to play The Joker in Christopher Nolan's 2008 superhero film Dark Knight, he was taking on more than just a role. In his way stood Jack Nicholson's Oscar-winning portrayal of The Joker in Tim Burton's Batman, a performance that still loomed large in the public imagination.
Ledger felt he had to entirely recreate the character, and lived alone in a hotel room for a month, formulating The Joker's voice, posture and personality. What emerged was a villain darker than anything yet seen in a mainstream action film, whom Ledger described as a "psychopathic, mass-murdering, schizophrenic clown with zero empathy".
Ledger himself was nowhere to be seen in this terrifying performance. It won him an Oscar -- sadly it was posthumous.
Michael Fassbender - Hunger
Irish actor Michael Fassbender is one of Hollywood's fastest rising stars, and he earned his reputation as a fearless and hugely talented actor in this gruelling, powerful film from artist and director Steve McQueen.
Hunger was set at the height of the 1981 hunger strikes at the Maze Prison, and Fassbender played the strikers' charismatic leader, Bobby Sands.
Fassbender dropped his weight to eight stone to play Sands in the latter stages of his torment, and, more importantly, brought real soul to his portrayal of a man who could not afford a moment's self-doubt.
It was a truly outstanding performance, and McQueen and Fassbender have since collaborating on another challenging project called Shame, a film about a New York sexaholic that will be released here in the New Year.