Then he won a movie role that offered him a terrifying glimpse of how his life could have panned out had he not conquered his drug demons.

After two spells in jail, Robert cleaned up his act, but his latest film led him to face up to his old life on the edge.

“I’ve been that train wreck, and I’ve been that person next to that person who could be a train wreck,” he said.

It’s been a year of living successfully for Robert, who hit movie gold with Iron Man and his outrageous performance in Tropic Thunder, which brought him a second Oscar nomination. The Iron Man dvd sales helped Marvel to record profits for the year.

But his new movie, The Soloist, brought him face to face with what might have happened if he hadn’t become clean and sober nine years ago.

He plays a journalist who befriends a down-and-out musician, played by Jamie Foxx.

Director Joe Wright opted to shoot part of the film among the real homeless and mentally-ill of Los Angeles, and those scenes still clearly move Robert.

“It turned into this incredibly, wonderfully humbling three months on Skid Row, which is probably exactly what I needed,” he admitted.

“I can’t think of anyone who doesn’t relate to the metaphor of derailment and just how awful and tragic that is.”

With a fast-talking personality he can barely contain, Robert, 44, has spent all his life in the glamorous but dangerous world of showbusiness.

His father, Robert, is a movie director and his son, blessed with talent, connections and good looks, started in movies as a teenager. He made The Pick-up Artist in 1987, putting him on the fringes of the Eighties Brat Pack.