Oscar nominee Robert Downey Jr. is expanding his theatrical repertoire - by writing a stage musical.

The star, who lost out on a Best Supporting Actor Academy Award on Sunday (22Feb09), has revealed he has been working on the project for a number of years, and is tirelessly trying to get it finished.

Downey Jr says, "I'm a little busy right now. Every two years or so I'm saying that I am going to do a big musical; I'm just tired of saying that I am going to do stuff that sounds cool. If I'm going to do something, I'm going to do it."

And he insists he isn't just trying to cash in on his fame and recent career resurgence - because he has always considered himself to be a musician.

The Iron Man star adds, "It's always lame when somebody gets really famous and they say they're going to be a singer. I'm like, 'You've already won the lottery, so take it easy, moron!' But I'm also a composer and I sing what I write."

Downey, Jr has already tasted a little musical success - his 2004 album The Futurist was well received and he also recorded a Christmas album with Vonda Shepard.