An industrious academic and charmingly eccentric Romantic poet and forger, Iolo Morganwg (1747-1846) left behind a floor-to-ceiling stack of unpublished manuscripts in his small Welsh cottage. "A Rattleskull Genius, " based on that trove of unpublished material now held at the National Library of Wales, provides both a celebration and a critical reassessment of the author and his contributions to Welsh cultural tradition.