In the Middle Ages, England had to contend with a string of usurpers who disrupted the British monarchy and ultimately changed the course of European history by deposing England's reigning kings and seizing power for themselves. Some of the most infamous usurper kings to come out of medieval England include William the Conqueror, Stephen of Blois, Henry Bolingbroke, Edward IV, Richard III, and Henry Tudor. Did these kings really deserve the title of usurper or were they unfairly vilified by royal propaganda and biased chroniclers? In this book we examine the lives of these six medieval kings, the circumstances which brought each of them to power, and whether or not they deserve the title of usurper.