This biographical work traces the life and career of Ademar of Chabannes, a monk, historian, liturgist and hagiographer who lived at the turn of the first Christian millennium. Utilizing the collection of over 1000 folios of autograph manuscript that Ademar left behind, this text reconstructs the development of Ademar's career and the events of his day. Richard A. Landes's research also elaborates on the realization (first articulated over 60 years ago by the historian Louis Saltet) that in 1029 Ademar suffered a humiliating defeat at the height of his career and spent his final five years producing a dossier of forgeries and fictions about his own contemporaries that succeeded in misleading historians from the 12th century right up to the 20th. This text systematically examines the evidence and the implications for the understanding of the period, offering an explanation of how these remarkable developments might have occurred.