Another person who used to be a hot leading man and has now settled into supporting mentor type roles is Kevin Costner, who I actually personally think is a better actor now than he was when he was young and popular. Or maybe he's a better supporting actor than a leading man. I used to think he was absolutely dull as a post, but he's enjoyable in stuff like Man of Steel, Jack Ryan Shadow Recruit, The Help, etc.
Actually he was pretty good as Pa Kent, he just had bad material. When kid Clark asks "can't I just keep pretending I'm your son?" and Costner hugs him and says "you are my son", that sounded more emphatic and emotional than hardly anything else I've ever heard Costner say in his life.