This is the first book-length study of fifteenth-century Castilian courtier Don Juan Pacheco. The biography uses contemporaneous and modern histories as well as unpublished archival materials to trace Pacheco’s long and controversial career at the court of Enrique IV of Castile. It explores how the powerful nobleman exploited his position as the king’s favorite in order to satisfy his political and personal ambitions and became the wealthiest and most titled courtier of the period. Through Juan Pacheco’s actions and objectives, the reader is given a portrait of the most successful of the fifteenth-century noblemen who competed with each other for power and riches in the era just before the reign of the Catholic Monarchs.