Leonardo DiCaprio on why he became an actor and what he really thinks about marriage.

“I feel like a whole era in my life is over,” Leonardo DiCaprio tells me. Tall and lanky, he’s one of the world’s biggest box-office stars, making $20 million a picture. But today he looks more like a young guy who just came in from doing yard work. He looks unhappy and tired.

“My grandma died last week,” he says quietly, explaining his pensiveness. “I have no more grandparents. I feel that coming ahead in my life is more stripping away, for sure. I feel very sad that Oma is gone.”

“Oma” was his maternal grandmother, Helene Idenbirken. Leonardo, 33, attended her funeral in Germany and just arrived back in L.A. He carries aviator sunglasses in his pocket, and when he goes outside later today, he’ll pull his cap down over his face. “It’s my paparazzi repellent,” he explains. He is in no mood for tabloid cameras.

“I always loved being with Oma,” he says. “She was completely pure, honest, unaffected, so unlike anything else that I was ever used to. She was my barometer of truth.” Helene and her husband and their daughter—Leonardo’s mom, Irmelin—were World War II refugees who suffered greatly. “Sometimes I’d ask Oma, ‘Isn’t it great now, all this stuff happening in my life?’ She’d say, ‘Don’t you worry about that. Take a break. Be a bricklayer. Work with your hands. You’ll love it. Step back and reflect on what’s going on in your life. Appreciate it.’ ”

DiCaprio leans across the table and grips my arm. “I do appreciate it,” he assures me. “I know how lucky I am.”

So, why did he become an actor? “We’re all after love, aren’t we? Love is what people are hungry for. That’s absolutely why I became an actor,” he admits.

In his new movie, Body of Lies, Leonardo plays a CIA agent up against terrorists. Directed by Ridley Scott and co-starring Russell Crowe, DiCaprio’s films invariably get Oscar buzz, and he’s received three nominations for his work in What’s Eating Gilbert Grape, The Aviator and, most recently, Blood Diamond.

But he remains best known around the world for the 1997 film Titanic.

“Titanic was a period of rebellion for me,” he says. “I was very much portrayed in the press as a heartthrob. It wasn’t what I wanted to be. It was like a runaway train. This thing just took off. I didn’t understand what was happening to me. My instinctive reaction to this tabloid madness was to want to run away.” For two years he stayed away from making movies, trying to ignore the media circus, protecting what he could of his private life.

“I am proud to have been in Titanic,” he says. “I’m grateful for the possibilities it’s given me. If it hadn’t been for that movie, I wouldn’t have been able to take control of my career. It was during that time that I started to think about things that meant more to the world than this glorified, superficial media exposure of me, something I never felt was justified.”

Looking for meaning beyond movies, DiCaprio got passionately involved in trying to help save the Earth. Putting his money where his mouth is, Leonardo today funds advocacy organizations and bankrolls a personal charitable foundation supporting environmental causes. 

“This is so much more important than anything,” he says. “I began to understand the huge crisis facing the human race. But we can feed all the starving people on the Earth, take care of the sick, and sustain the planet we’ve inherited. And if it happens, won’t it be amazing? Stopping the destruction? I get overwhelmed just talking about it!”

Over the years, Leonardo has had romantic relationships with a series of exceedingly beautiful women, principally models. His turbulent affair with Gisele Bündchen lasted nearly five years. They split up in November 2005. Most recently, he’s been involved with a stunning Israeli model, Bar Refaeli, 23. They have been a couple, on and off, for two years.

“It’s hard to talk about this stuff,” he says. “I want to keep some of this for myself. When we talk about ourselves, we know the bad parts, too.”

In the past, Leonardo has refused to discuss his romantic relationships, explaining that he has “few emotions,” has “never been in love,” and “does not believe in marriage.”

I ask if he still believes what he once said.

“No, I don’t agree with any of that,” he replies. “It sounds like the ignorance of youth to me. When did I say that? Three or four years ago? Hey, we grow up real fast.

“What I definitely feel a need for is to make my life about more than just my career,” he continues. “Just last night I was thinking to myself how little of my life has been lived normally and not spent on some far-off movie location. I want to get married and have children. In saying that, I realize I am contradicting everything I’ve said before. I absolutely believe in marriage.”

He puts on his sunglasses and adjusts his baseball cap. “I hope I never get cynical,” he says before he leaves. “I think you need youthful energy, excitement, and optimism in life. There is a lot I want to do, and the more cynical you become, the more you sit on your butt and do nothing. The one thing that I would love is to never become cynical about the things I think are really important, like family, like the environment.” He smiles. “What I want is to be known as someone who stood for something.”