Musicians: no acting experience necessary

I've long been fascinated by what prompts a musician to pursue an acting career. Do most of them assume that their personae will remain compelling when transposed to another medium? What combination of lucre, hubris, and desire for world conquest motivates them?

I rank the five best. If you think Bogart and Christopher Walken have had uneven career arcs, you haven't looked at Frank Sinatra or Liza Minnelli's.