The OP is referring to Robert Downey Jr, whose comment is here:

Gore Vidal wrote an excellent novel around 1962, about an emperor, Julian. I believe he was just after Constantine and Constantius, so roughly 4th Century Common Era (A.D.). I'm too old to play him, but it's an incredible story.

(I mention this since to me, RDJ is the musician Richard D. James, aka Aphex Twin)