Robert Downey Jr. says settling down has been key to his Hollywood comeback.

The 'Iron Man' star revealed his marriage to Susan Levin is the secret to a happy life, and leaving his wild past behind has made this his best year yet.

The 43-year-old actor said: "This is probably the most back-breaking, a**-kicking work year I've ever had. It's also been the most manageable year I've ever had I feel now that I can leap buildings in a single bound, but I'm not underestimating how difficult it is. Life is really, really hard, and I need to stay focused on the day-to-day stuff."

After a promising Hollywood career, including an Oscar-nominated performance in 'Chaplin,' Downey succumbed to drink and drugs, culminating in various stints in prison and rehab.

Since marrying Susan in 2005, Downey has been working his way back to the top, but says he will never forget the dark days.

Downey added to Britain's Daily Mirror newspaper, "I'll never forget that time I was in the gutter. It's important that I often remind myself of that, so it never happens again."

'Iron Man' opens in cinemas worldwide today, and also stars Gwyneth Paltrow, Jeff Bridges and Terrence Howard.

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