In "Tropic Thunder, " a comedy about self-absorbed Hollywood types making a "Platoon"-style war movie, Downey plays Australian actor Kirk Lazarus, a multiple Oscar-winning performer who gets so involved in his roles that he forgets to come out of them.
The actor, now aged 83, is taking the stage on Thursday to converse with fellow performer Nicholas Parsons about his career, with clips from some of his funniest sequences being shown.