Who is Richard Madoc, from "Calliope" from The Sandman and what is their importance?

Richard Madoc is a self-serving writer who gets what he deserves in the story "Calliope." Madoc trades a supposedly mystical stone for the muse Calliope. He holds Calliope captive and rapes her so that he can cure his writer's block and write inspired epic books, poems, plays, and films. Madoc dehumanizes Calliope by telling himself that she is not a human being, and therefore she is not a person. He rationalizes his treatment of her by imagining that Calliope's feelings don't matter, since she is not "real." He gains wealth and fame through his actions and is unable to give them up.