Harthacnut was the last of three Danish kings to rule in England between 1013 and 1042. Although he was king of Denmark for many years, Harthacnut only ruled England directly for the last two years of his life. Yet he shaped the course of English history most profoundly. Because his mother was Emma of Normandy, Harthacnut ensured that Emma’s son by a previous marriage, Edward the Confessor, should succeed him as king of England. This established the Norman claim to the English throne. An understanding of Harthacnut’s adventurous career, his complicated family relationships, and the manner in which he created a northern empire based upon sea power and trade now enables us to appreciate more fully why the Norman Conquest of England came about.