Hugo O'Conor: A Shadow of Ireland in New Spain presents a comprehensive biography of Hugo O'Conor (1734–1779), the first Commandant Inspector of the Interior Provinces of New Spain. Demonstrating the remarkable breadth of O'Conor's life experiences, the narrative moves from his early life in Ireland to a successful career in the Spanish military spanning both sides of the Atlantic. O'Conor's story reads like an action-packed nail-biter. He grew up on "the Isle of Slaves," as Ireland has been characterized, but had to flee due to the imposition of the anti-Catholic Penal Laws of the eighteenth century. He entered the Hibernia Regiment of the Spanish army and subsequently found himself immured in a rigid military caste system at the age of fifteen. O'Conor went on a wide array of adventures: fighting a brutal—but largely forgotten—war in Portugal; serving as a drill master in Cuba; becoming a spy and then governor in Texas; and implementing the crown's plans of military reform in northern New Spain, becoming feared by Apaches across the Southwest Borderlands. Finally settled after his travels, he became an effective governor of Yucatán during the same period as the American Revolution. Author Mark Santiago's Hugo O'Conor makes its principal contribution to borderlands history by showing how O'Conor played a crucial part in the development of Spanish military power in what is now the American Southwest. Perhaps even more importantly, this work captures the humanity of O'Conor and his times. Hugo O'Conor is an enticing blend of artistic storytelling and academic rigor that advances our understanding of the military and political landscape of the Spanish Colonial period, especially in the Texas–Mexico borderlands.