"It was a very risky undertaking. I can't tell you how many people said to me, 'this is my favourite book of all time'. Not many projects will arise where people have that expectation and want to see you dramatise scenes they have stuck in their head," DiCaprio says. "But then I re-read the book and I became re-fascinated by Gatsby. And combined with the partnership of Tobey [Maguire] playing Nick Carraway and Baz directing, both of whom I've known over 20 years as trusted collaborators, I then accepted the role. But there was a tremendous amount of hesitation initially."
His face creases into that familiar grin. "Actually, Baz is a bit of Gatsby himself," he says.
"He is the manifestation of his own dreams and he's one of the most infectious directors I have ever met, as far as his enthusiasm for doing great art. You cannot get in a room with Baz and not feel nostalgic for the world that you're going to create."
DiCaprio says that he knew as soon as Luhrmann handed him the book he wasn't going to say no. "By merely being in the room with Baz, it was inevitable. You get caught up in the whirlwind that is Baz Luhrmann and it is incredibly exciting."
The pair first met when DiCaprio was a teenager. "When I was 18 and I flew to Australia to do a test rehearsal for Romeo + Juliet; he was a very risky film-maker.
He didn't want to take on simple stories, he wanted to do Romeo + Juliet and do an entirely different universe for it; the same thing with The Great Gatsby. They are incredibly risky undertakings. I admire that in him."
DiCaprio hasn't changed much from the shy young man I first met in New York at the 1997 press junket for Romeo + Juliet. Even as an awkward teenager there was an air of elegance about him - he was composed and spoke thoughtfully with carefully measured words. In many ways, he's akin to a politician more so than a Hollywood movie star.
This afternoon at New York's Plaza Hotel, DiCaprio talks about feeling more comfortable in his skin these days. "I suppose it's something that comes with age.
I've grown up in this industry, I've been acting ever since I was 13 years old and, in a lot of ways, I've grown up on screen and in the public eye. I suppose, now that I have two more years of desperately holding on to my 30s," he laughs, "the realisation that I've been on this grand journey to fulfill my childhood dreams has hit me."
At first glance, it would appear that DiCaprio's life of wealth - he reportedly earns an average salary of US$20 million ($24.6 million) a movie, attends extravagant parties all over the world and has had a bevy of glamorous women on his arm over the years - could be a page taken from Jay Gatsby's life. However, he insists that life isn't what it seems.
"The truth is, my life is much different to Gatsby's. He throws these lavish parties where everyone in the world wants to be and they want to connect with him and show up and join in the fun, but Gatsby is somebody who erased his past and left all those connections from his humble beginnings," he says. "For me, in my life, I have grown up with great family and friends surrounding me, and they are still with me."
An only child, DiCaprio was born in Los Angeles. His German-born mother, Irmelin, was a former legal secretary, and his father George, whose family originally hails from Naples, was an underground comic artist and distributor of comic books. His parents divorced before his first birthday and he was raised primarily by his mother, who worked several jobs to support them in working-class neighbourhoods such as Echo Park and Los Feliz.
It's believed his name was settled on when his pregnant mother felt her first kick while looking at a painting by da Vinci. "My mum said that she and my dad were at the Uffizi Gallery in Florence, and when she felt me kicking in the womb, my dad said, 'His name should be Leonardo'."
Much has been made of DiCaprio's high-profile romantic endeavours. He's been in relationships with a string of glamorous partners, most notably Victoria's Secret models Gisele Bundchen, from 2001 to 2005; Bar Refaeli, from 2005 to 2007; and Erin Heatherton, from 2011 to 2012. In between, there was a brief relationship with another leggy blonde, actress Blake Lively. To his credit, he never talks in specifics about his love life.
Often described by his peers as overly generous, when he landed the role in Romeo + Juliet he cashed in his business-class ticket for economy seats so his friends could accompany him to Australia to shoot the film. However, when it comes to women, he's not one to shower them with diamonds and extravagant gifts in an effort to sweep them off their feet.
"I think that women ultimately don't respond to those things," he says. "I think most importantly they have to feel comfortable with you, so I just be myself. I think there's a lot of speculation from men as to what women are attracted to and there's a lot of misconceptions. Women of quality don't care about those things."
He resides between his home in Los Angeles and an apartment in Lower Manhattan. He also owns an eco-friendly building overlooking the Hudson River in Manhattan, and bought an island off mainland Belize, as one does when one is a bona fide movie star.
Away from his acting life and production company, Appian Way, DiCaprio's other passion lies in his environmental work. He narrated and produced the documentary 11th Hour, in which he cited global warming as "the number one environmental challenge", and recentlyraised US$38 million at a contemporary art auction at Christie's in New York, the proceeds of which will fund global conservation projects to create sanctuaries to save endangered species.
Despite naysayers, he's helped bring awareness to this worldwide issue, and it's an interest that began years before it became Hollywood's cause celebre. But not surprisingly, because of his status, he's come under some criticism.
"I don't care who gets called a hypocrite. I try to live green as much as I can. I have solar panels. I've been driving a hybrid car for many years. [He drives an electric Tesla Roadster, Fisker Karma, and a Prius.] Yes, I have to fly commercial airlines for my work, but I have built my house green."
DiCaprio has endured a love-hate relationship with his celebrity. However, he learned quickly how to put his name to good use. A generous philanthropist, he's donated funds to many worldwide causes, including orphaned children from Mozambique, and gave US$1 million to relief efforts in Haiti after the earthquake in 2010. A gay rights activist, last month he donated US$61,000 to the GLAAD foundation.
Despite a slew of awards, the one honour that continues to elude him is an Academy Award. "Is it a dream?" he says, rhetorically. "Well, I don't think anyone would say that they wouldn't want one, or they'd be lying, but it's not my motivation when I do these roles. I really am motivated by being able to work with great people, and create a body of work for myself that I can look back on and be proud of."
First nominated in 1993 at the age of 19 for What's Eating Gilbert Grape, he recalls his experience at the Academy Awards. "I didn't really understand what was going on at the time and I was shell-shocked by the whole experience. My mother was incredibly excited, as was my father. I remember them saying to me, 'do you realise what just happened?' I was like, 'I guess, yes'." He laughs. "But I didn't understand the magnitude of it. I was incredibly shy to go to the actual ceremony and that's what I remember most."
He seems content to bide his time until he gets the chance to accept the golden statue.
Perhaps The Great Gatsby will be the one to bring it home for him?
He pauses. "The truth is, I have learned through my experience in this industry that there is absolutely no way to control or do anything as far as people's opinions on your performance or a movie. You go out there and you promote your film and you hope people like the work that you did. But they're going to respond the way they're going to respond. And when they're in a room with that ballot, who knows?"
Appreciative of this time in his life, his good fortune isn't lost on him. "I still feel that I won the lottery because I'm doing what I love for a living. When I started out, I was living in Hollywood and I wanted to become an actor but I never felt like I belonged. When I got my foot in the door I was able to start this journey that has led me to the place I'm now at. I'm still excited to be here. I don't take it for granted."
• The Great Gatsby is in cinemas on June 6.
