Isabella of Castile (1451-1504) was a significant monarch in Spanish history. She became Queen of Castile in 1474 and is best known for her marriage to Ferdinand II of Aragon, which united two of the largest kingdoms in Spain. Together, they completed the Reconquista by capturing Granada in 1492, marking the end of Muslim rule in the Iberian Peninsula. Isabella is also famous for sponsoring Christopher Columbus's voyage in 1492, which led to the discovery of the Americas. Her reign is often associated with the establishment of a unified Spain and the beginning of its global exploration and colonization efforts.