Which monarchs instituted the Spanish Inquisition?

Ferdinand II of Aragon and Isabella I of Castile instituted the Spanish Inquisition. Together they are known as the Catholic Monarchs, and their reign marked a major expansion of royal power in late-fifteenth-century Spain.

In 1478, Ferdinand and Isabella asked Pope Sixtus IV to authorize a new inquisition for their realms. The pope’s approval allowed the monarchs to nominate inquisitors, giving the Spanish institution a much stronger royal character than the medieval inquisitions that had operated primarily under papal authority.

The first inquisitors, Miguel de Morillo and Juan de San Martín, were appointed in 1480. The institution initially concentrated on conversos—Jews who had converted to Christianity but were suspected of secretly maintaining Jewish practices. It later investigated Muslim converts, Protestants, alleged heresy, and other religious offenses.

Ferdinand and Isabella were not the same people as Ferdinand III or Charles V. Ferdinand II ruled Aragon, while Isabella I ruled Castile; their marriage united their dynastic interests but did not immediately merge their kingdoms into a single state. The Inquisition became one of the tools through which they strengthened authority across both realms.