At the age of 30 Leonardo DiCaprio has the air of a man who has achieved all he ever wanted in his acting career - and much more besides. Sought out by the best directors, his major credits include Gangs of New York, Catch Me If You Can, The Beach, Celebrity, Titanic and William Shakespeare's Romeo + Juliet. Not bad for a man whose movie debut came in Critters 3: You Are What They Eat. In The Aviator he plays Howard Hughes, a man possessed by a drive for perfection and demons that would eventually overwhelm him.

How would you describe the Howard Hughes you portray in The Aviator?

He was a man obsessed with everything that he put his mind to. He was relentless and would not stop until he had reached his own ideals of perfection - that might be creating a bra for Jane Russell or building the Spruce Goose aircraft, or sleeping with as many women as he possibly could, or breaking speed records. I was interested in that element of a character obsessed, who was then confined in his own private, mental hell by this aversion to microscopic germs. I thought that made for one of these characters no writer could possibly have made up.

Is it true you found the book upon which John Logan's script is largely based?

I stumbled upon it, and I guess you could say I became obsessed about wanting to play him. We deliberately focus on his earlier years, and deal with a man at the onset of his own madness rather than in its aftermath. So you have this great see-saw act where he's succeeding in all these different departments and living out all the dreams he had when he was a young man. It's like a test case for what happens when you give someone everything in the world as he fulfils all these dreams while simultaneously being gripped by this mental illness.

Were you able to do a lot of research on such a reclusive figure as Hughes?

Well first of all we were playing characters here. We said we wanted to be as authentic as possible but at the same time create our own characters out of the actual events. I read as many books as I could, and met people who knew him like Jane Russell and his ex-wife Terry Moore. But the main thing that really helped me in capturing his character was the documentary footage of the Senate hearings. There is other footage of him but he's such a private man that whenever he spoke about something it would be very specific. He was like a robot, very technical.

The Senate hearings made him a huge public hero didn't they?

He was a billionaire - America's first - so he was a powerful man, but there he was an individual taking on a corporate monopoly and the Senate. When he succeeded there was a huge grass roots effort for a while to make him President.

How would you rate his efforts as a filmmaker?

Well The Outlaw is pretty horrendous. They literally did hundreds of takes before he got what he wanted. I don't think it even had to do with performance, it was probably the way somebody said a line, or the angle on somebody's face or the way a piece of wardrobe looked. He spent millions of dollars on that movie. It's interesting to watch a man with obsessive compulsive disorder make a film. That was quite apparent on Hell's Angels, having him shoot that movie for four years and re-shoot it for sound and spend more money that had ever been spent on a feature film in history.

Did you ever feel the urge to follow in his flight path and take to the skies yourself?

I asked if I could go up and fly in some of these planes but the insurance company quite understandably said absolutely not, they wouldn't allow me to fly for the first time in antique war planes a couple of weeks before shooting. So I understood that. But I got to simulate what it was like to fly one of those planes. That's the great thing about making a movie, you learn about the subject, you simulate the experience and get into the history of it all. For Howard Hughes' character to be up in the sky like that, cocooned from the world and in control of his own vehicle, in his own germ-free zone in the heavens, that was his favourite place to be.

Cate Blanchett, as Katharine Hepburn, delivers a poignant speech about the downsides of fame. Is that something you could particularly identify with?

There are pros and cons to everything. To be able to do what I do and what I love on this level is a very positive thing. There are certain invasions of privacy, but I hate sitting around complaining about it, I just don't like to hear it come out of my mouth. I'm a very fortunate person being able to do what I do.

The Aviator is released in London's West End on 26th December 2004 and in UK cinemas nationwide on 6th January 2005.