Movie star autobiographies generally promise far more than they deliver, but the memoirs of Robert Downey Jr may well prove to be an exception.

Now 41, the actor, whose turbulent life includes serving time in prison for drug offences, has signed a publishing deal with HarperEntertainment, which plans to have the book in stores by 2008. Downey Jr will be back on our screens next month, with Keanu Reeves, Winona Ryder and Woody Harrelson in Richard Linklater's A Scanner Darkly (pictured above).