What is the author's purpose in the novel, William the Conqueror?

William the Conqueror tells the rags-to-riches story of an orphan who became one of medieval Europe's most powerful rulers. Drawing upon the few known facts about William's life, Costain uses both his skill as a novelist and his knowledge of history to paint a rounded picture of a man seemingly born to be a leader. Costain's account of William's life—his narrow escapes from assassination as boy, his training to become a knight, and his military campaigns in England and France—reads like an adventure story. All in all, Costain takes a familiar figure from history, breathes life into him, and shows the elements of character that made William a great king. Additionally, Costain informs his readers about the nature of life in the Middle Ages, describing the food, the clothing, and the uncomfortable living conditions that even the most powerful and wealthy individuals had to endure.