Queen Isabella I ruled Castile and Aragon jointly with her husband, Ferdinand (Ferdinand II of Aragon, Ferdinand V of Castile).
In 1480, Isabella and Ferdinand instituted the Inquisition in Spain, one of many changes to the role of the church instituted by the monarchs. The Inquisition was aimed mostly at Jews and Muslims who had overtly converted to Christianity but were thought to be practicing their faiths secretly -- known respectively as morranos and moriscos -- as well as at heretics who rejected Roman Catholic orthodoxy, including alumbras who practiced a kind of mysticism or spiritualism.
Isabella and Ferdinand proceeded with their plans to unify all of Spain by continuing a long-standing but stalled effort to expel the Moors (Muslims) who held parts of Spain. In 1492, the Muslim Kingdom of Granada fell to Isabella and Ferdinand, thus completing the Reconquista. That same year, all Jews in Spain who refused to convert to Christianity were expelled by royal edict.Also in 1492, Isabella was convinced by Christopher Columbus to sponsor his voyage of discovery. The lasting effects of this were many: by the traditions of the time, when Columbus discovered lands in the New World, they were given to Castile. Isabella took a special interest in the Native Americans of the new lands; when some were brought back to Spain as slaves she insisted they be returned and freed, and her will expressed her wish that the "Indians" be treated with justice and fairness.
Isabella was also a patron of scholars and artists, establishing educational institutions and building a large collection of art works. She learned Latin as an adult, was widely read, and educated not only her sons but her daughters. One of these daughters, Catherine of Aragon, is known in history as the first wife of Henry VIII of England and mother of Mary I of England.