Tomás de Torquemada[a] OP (14 October 1420 – 16 September 1498), also anglicized as Thomas of Torquemada, was a Roman Catholic Dominican friar and first Castillian Grand Inquisitor of the Tribunal of the Holy Office, which was a group of ecclesiastical prelates created in 1478 and charged with the somewhat ill-defined task of "upholding Catholic religious orthodoxy" within the lands of the newly formed union of the crowns of Castile and Aragon, presently known as the Kingdom of Spain.

In part because of persecution, Muslims and Jews in Castile and Aragon at that time found it socially, politically, and economically advantageous to convert to Catholicism (see Converso, Morisco, and Marrano).

[3] This led Torquemada, who himself was believed to have had converso ancestors,[4] to be one of the chief supporters of the Alhambra Decree that expelled the Jews from the Crowns of Castile and Aragon in 1492.

Owing to the Inquisition's use of torture to extract confessions and burning at the stake of those declared guilty, and to Torquemada's own approval, even advocacy, of these practices, his name has become synonymous with cruelty, religious intolerance, and fanaticism.

He was present at Isabella's coronation in 1474, remained her closest ally and supporter, and even advised her to marry King Ferdinand of Aragon in 1469 to consolidate their kingdoms and form a power base he could draw on for his own purposes.

King Ferdinand and Queen Isabella petitioned Pope Sixtus IV to grant their request for a Holy Office to administer an inquisition in Spain.

Henry Charles Lea observed that the Spanish Inquisition in both Castile and Aragon remained firmly under Ferdinand's direction throughout the joint reign.

[18] As Grand Inquisitor, Torquemada reorganized the Spanish Inquisition (originally based in Castile in 1478), establishing tribunals in Sevilla, Jaén, Córdoba, Ciudad Real and (later) Saragossa.

The Spanish chronicler Sebastián de Olmedo called him "the hammer of heretics, the light of Spain, the savior of his country, the honor of his order".

Hernando del Pulgar, Queen Isabella's secretary, wrote that 2,000 executions took place throughout the entirety of her reign, which extended well beyond Torquemada's death.