I'm starting to lean towards this. I figured middleaged would be older than 40, but he's kind of the only one mentioned who would be considered world famous/superstar. Charlie's been more of a joke the last few years.

Whoever it is, he is still acting. When he's not acting, he apparently 'hides away' and keeps to himself, so that wouldn't work with Leo because he's out and about with his gf all the time.