Ego maniac Robert Downey Jr.

Robert Downey Jr. struggles to control his ego. 04/20/2009 - Robert Downey Jr. - The 'Soloist' actor finds it difficult to remain levelheaded about his career and often has to remind himself acting is just a job. © David Gabber / PR Photos

04/20/2009 - Robert Downey Jr. - The 'Soloist' actor finds it difficult to remain levelheaded about his career and often has to remind himself acting is just a job. © David Gabber / PR PhotosThe 'Soloist' actor finds it difficult to remain levelheaded about his career and often has to remind himself acting is just a job.He explained: "It's always about ego. My challenge is to hold my own space and remember what purpose I'm serving. And I'm serving a purpose. My purpose is to be of service."After recently starring in hit movies 'Iron Man' and 'Tropic Thunder', the 44-year-old actor admits he almost let his stardom get the better of him.He explained: "You have a billion-dollar box office year and you start wondering if there isn't more to you. Maybe I'm more than I thought? Nope!"In 'The Soloist', Robert plays a Los Angeles journalist Steve Lopez, who befriends a homeless musician and shares his story with the city.The star has revealed he had to follow strict rules while making the movie, which also stars Jamie Foxx.He explained: "Don't be endomorphic and talk too much. Don't be too funny. We don't need any sexy beats here. You know? And it's not heart wrenching soul-stripping drama. It's a story. It's a character study. And it's a character study of someone who is not a character. It's a character study of someone who is studying someone else."