For me, the plum role in any move is the producer. The one who calls the shots, who gets to choose the script, the cast, the director and everything else in between.
Learning lines? Not for me. Script re-writes? As long as I am the one that orders them. Explain character motivations? include me out.
I would want to be one of the old-school guys, like David O Selznick, launch a search for Scarlett, or have beauty kill the beast. I want my name to be displayed over the title in the opening credits
I like that the producer can be realistic, no need to bore endless interviewers with self-aggrandising discussions of artistic effort or technical bravura – enough for me would be that the movie is made, the story is told, all the threads drawn together and tied up in to a pack of magic that audiences will love.