LOS ANGELES – To transform himself into an aging J. Edgar Hoover, Leonardo DiCaprio sat for hours at a time while makeup artists gave him liver spots, yellow teeth and big, bulbous love handles. He spends a good chunk of Clint Eastwood’s film “J. Edgar” that way, sweating and sneering in the unforgiving lighting of FBI headquarters.

The part also meant memorising endless monologues that needed to be delivered with Hoover’s own breakneck cadence. Additionally DiCaprio, who typically comes accessorised with a super model girlfriend in real life, had to wrestle aggressively with a man and then kiss him.

Oh, and wear a dress.

Faced with a role with demands like that, most superstar actors, even those eager to catch the attention of Oscar voters, would have turned and run. Look unhandsome and unheroic? Too big a risk, even with Eastwood at the wheel. But DiCaprio, at least the post-“Titanic” one, has made a career of highly risky choices, and somehow it keeps paying off not only on the awards circuit – he has been nominated for three Academy Awards – but at the box office as well.

“When I can’t immediately define the character, and there’s an element of mystery to it and still a lot to be explored, that’s when I say yes,” the 36-year-old DiCaprio said in an interview recently on a patio at the Hotel Bel-Air here. “I like those kinds of complicated characters. I just do.”

Hollywood typically doesn’t like that answer. The star system may have become more subtle since the days of Clark Gable and Jimmy Stewart, but it’s still a system: U.S. actors are supposed to be more steady persona, less shape shifter.

“The apparatus likes to box actors up,” said Brian Grazer, a producer of “J. Edgar,” which was released recently. “Once they become successful in one role, get them into picture after picture where they can do exactly the same thing.”

Grazer added: “To resist that, you have to make very hard choices. Most people are too afraid.”

It probably helps that DiCaprio has managed to retain a mystique about his personal life in the celebrity blogger era. Keeping that distance is something he works on. In an interview, for instance, he didn’t pretend to be a friend the way a lot of stars do. He likes his privacy, but this game also makes his performances more successful; people are more likely to accept him as a larger-than-life character if they don’t have a very clear idea of who he is off screen.

DiCaprio’s choices may be unusual, but he does have his own version of sticking with what works. The characters are mostly tortured, unsympathetic, larger-than-life guys created with the help of a tiny club of A-list directors, most notably Martin Scorsese. A urine-collecting Howard Hughes in “The Aviator.” A Zimbabwean smuggler in “Blood Diamond.” A mental patient in “Shutter Island.” A dream extractor in “Inception.”

“Leonardo could make a lot of money making mechanical genre pictures, but he wants to be challenged,” Eastwood said by telephone. “And it’s much more of a challenge to play someone who doesn’t have the slightest thing in common with you.”

Next on DiCaprio’s docket is the title role in Baz Luhrmann’s remake of “The Great Gatsby,” and he’s ready to play Frank Sinatra in another Scorsese biopic.

“That is in Mr. Scorsese’s hands,” he said of a potential Sinatra film, pausing to pop a wedge of watermelon into his mouth and pour himself another cup of coffee. “I’m always incredibly game for anything that he decides to do.”

“J. Edgar” fits snugly into this canon. The best biopics offer a portrait of person, warts and all, and invite viewers to make their own judgments about him, and Eastwood’s film strives to do just that. Hoover is depicted as a brilliant patriot who invented modern forensics and stopped at nothing to protect America through eight presidents and three wars. But the omnipowerful FBI director was an impediment, to put it mildly, to the civil rights movement and worked as hard to distort the truth as he did to collect it (and file it away) to secure his power.

All of that is more or less fact. The treacherous part of “J. Edgar,” written by Dustin Lance Black, an Oscar winner for his “Milk” screenplay, involves the gray. Was Hoover gay? Nobody knows for sure. He certainly had an unusually close relationship with his FBI colleague Clyde Tolson, played in the film by Armie Hammer (“The Social Network”). Even less clear is whether Hoover liked to wear women’s clothes, but Eastwood and DiCaprio decided to retain Black’s artful nod to the rumour.

“Obviously there’s a love story here,” Eastwood said. “Whether it is a gay love story or something else – well, the audience can interpret it. My intention was to show two men who really love each other, and beyond that it’s none of my business.”

DiCaprio’s risk taking is cheered by the Hollywood contingent that loves serious films, raising him to the level of deity for his willingness to make the kind of drama that is an endangered species at major studios these days. But a more business-minded crowd – agents, studio chiefs – says taking on all of these biopics is a mistake. The worry is that at some point DiCaprio will become uninteresting to audiences if he doesn’t pepper his road with a wider variety of roles.

Jeanine Basinger, chairwoman of the film studies department at Wesleyan University, calls this “the Paul Muni problem.” Muni was perhaps the top actor at Warner Brothers in the 1930s, starring as powerful characters in films like “Scarface.” He also had a penchant for biographical parts, winning an Oscar for “The Story of Louis Pasteur” (1936). But he developed a type of obsession with historical roles and faded.

Does DiCaprio worry about boxing himself in by trying to stay out of the box? If he does, he’s not admitting it.

“Never. No. I don’t,” he said quickly.

Although Basinger raises the point, she’s not terribly worried herself. Few other actors have as much raw talent as DiCaprio, she noted, and the fact that he has been able to move from the 1980s sitcom “Growing Pains” to “What’s Eating Gilbert Grape” to “Titanic” to “The Departed” bodes well for his future growth.

“He is always very strongly present as DiCaprio, yet he can really make us believe that he is another person,” Basinger said. “That’s incredible talent.”

DiCaprio’s Oscar nominations have been for “What’s Eating Gilbert Grape,” which he made when he was 19 years old, “The Aviator” and “Blood Diamond.” Veteran awards strategists (not working on behalf of “J. Edgar”) think he is a shoo-in for a nomination this year, along with George Clooney for his role in “The Descendants,” Alexander Payne’s look at a man trying to reconnect with his two daughters after his wife falls into a coma. But it’s still too soon to tell whether another Academy Awards ceremony is in DiCaprio’s immediate future.

Will “J. Edgar” be a hit? Also unclear. But DiCaprio does have an insurance policy in that ever pesky “Titanic,” which will be re-released in April in 3-D. If a 3-D conversion of “The Lion King” can generate almost $100 million, as it did for Disney in October, “Titanic” should easily make a major box office splash.

DiCaprio said he hadn’t thought about it much and had come to terms with being continually associated with the dopey Jack Dawson.

“I’m not haunted by it, but it certainly follows me,” he said. “I’ve been to the Amazon, and people with no clothes on, and I’m not exaggerating, know about that film. I’ve accepted it.”