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

Calliope is the youngest muse, known for her beautiful voice. She is the muse who inspired Homer to write his epic poems. In 1927, Erasmus Fry captures Calliope and holds her captive, raping her to force her to inspire him. Fry becomes a famous author. When he is in his eighties, Fry trades Calliope to another writer, Richard Madoc, in exchange for a bezoar to protect him from poison. Calliope is held captive, helpless, as Madoc's muse until Oneiros saves her.