To my surprise, Ed Witten, one of the preeminent physicists of our time, is quite gifted in public talks and interviews from what I've seen of him. You'd expect someone explaining string theory to laymen to throw in a few "ums," but they're quite rare in this and other interviews (https://www.youtube.com/watch?v=f1BcyxQCnoE&feature=rela...). I find it inspiring, as someone who's had issues with public speaking in the past, to see such a brilliant man handle a conversation with such ease.