I've been very lucky to have achieved a lot of the things that I dreamt of achieving as a young man. But, at the end of the day – and I truly believe this – it is not about achieving great wealth or success. Because they don't bring happiness ultimately. They really don't. What matters is whether or not you've fulfilled the idea of having led an interesting life, whether you've contributed in some way to the world around you.

The challenge is to understand the psyche of somebody like that. There is no true genius or revolutionary ideas, I don’t think, without some element of compulsiveness or madness or obsession, and that’s certainly indicative of Howard Hughes. Understanding his obsessive-compulsive disorder was really the key for me for opening up who this man was.

On turning 30: "I kind of feel like the same person except more time has gone by. I hate to say that I feel like an adult now. I have to admit I wish I was still 18. After all, even through the time while I was representing that wild kid, I really wasn't. I was just living my life. I was just not making movies at the time.

The last thing I want to turn into is a fat Hollywood jerk. I was brought up without much money and I was happy. I don't think that I will strive for money or success and end up greedy or big-headed. That only leads to unhappiness. I can still be down-to-earth and do this job as long as I enjoy it.

As an actor, you're constantly searching for that great character. Also, being a history buff and learning about people in our past and amazing things that they've done, I came across a book about Howard Hughes and he was set up as basically, the most multi-dimensional character I could ever come across. Often, people have tried to define him in biographies, but no one seems to be able to categorize him.

I don't really have many extravagances. I don't fly private jets and I don't have bodyguards and I don't buy crazy things. I have a couple of houses here and there. I bought a very expensive watch, and I am going to buy a really expensive movie poster, the original for The Thief of Bagdad (1940). I love movie posters.

"I was behind a woman at the checkout counter who was looking at the magazines. She turned to me and goes, 'There he is again, that Leonardo DiCaprio. Don't you wish he'd just disappear?' I said, this is the moment where I either go, 'Do you know who I am?' or put my hat further down, pay for my corn-nuts and get out of there....I choose to avoid that. (2005)