This book examines the rise and fall of the aristocratic Lacy family in England, Ireland, Wales and Normandy. As one of the first truly transnational studies of individual medieval aristocrats, it provides a fresh look at lordship and the interplay between aristocracy and crown from 1166 to 1241. Hugh de Lacy (d.1186) traded on his military usefulness to King Henry II of England in Wales and Normandy to gain a speculative grant of the ancient Irish kingdom of Mide (Meath). Hugh was remarkably successful in Ireland, where he was able to thwart the juvenile ambitions of the future King John to increase his powers there. Hugh was hailed by native commentators as 'lord of the foreigners of Ireland' and even 'king of Ireland'. In this study, his near-legendary life is firmly grounded in the realities of Anglo-Irish politics. The political career of Hugh's less famous son and heir, Walter de Lacy (d.1241), is in turn illuminated by surviving royal records and his own acta. Walter was one of the major players in the Irish Sea province under Kings Richard I, John and Henry III, and his relationship with each king provides a unique insight into the nature of their reigns. Over the course of fifty-two years, Walter helped to shape the course of Anglo-Irish history. That history is recast in the light of the transnational perspective of its chief participants. This book is especially useful for those studying the history of medieval Britain and Ireland, and is a major contribution to current debates over the structure of medieval European society.