Alonso de Salazar Frías has been given the epithet "The Witches’ Advocate" for his role in establishing the conviction, within the Spanish Inquisition, that accusations against supposed witches were more often rooted in dreams and fantasy than in reality, and the inquisitorial policy that witch accusations and confessions should only be given credence where there was firm, independent, corroborating evidence. He was probably the most influential figure in ensuring that those accused of witchcraft were generally not put to death in seventeenth- and eighteenth-century Spain. The Spanish Inquisition was one of the first institutions in Europe to rule against the death penalty for supposed witches. Its Instructions of 1614, which embodied Salazar's ideas, were influential throughout Catholic Europe.
Alonso de Salazar Frías (c. 1564–1636) was born in Burgos, where his father was a lawyer and belonged to an influential family of civil servants and prosperous merchants. Salazar studied for degrees in canon law at the University of Salamanca and at the University of Sigüenza. He took holy orders and was appointed as a vicar-general and judge at the court of the bishop of Jaén. His career owed a great deal to his close relationship with Bernardo de Sandoval y Rojas, Bishop of Jaén, and subsequently Archbishop of Toledo. Having gained a reputation as a successful lawyer, Salazar was elected Attorney General of the Castilian Church in 1600. When his patron became Inquisitor General in 1608, Salazar was selected as an inquisitor for a vacant post at Logroño (La Rioja) in 1609. His intelligent and single-minded approach to the witch trials conducted by this tribunal created great respect for him within the Inquisition. He became a member of its Supreme Council in 1631.
When Salazar joined the tribunal of Logroño as its third inquisitor in June 1609, preliminary hearings were already under way in what was to prove the biggest series of witch trials in Spanish history, eventually involving 1384 supposed child witches and 420 supposed adult witches. This was a witch persecution unmatched in scale, before or after, in Spain. The accused in these trials came almost exclusively from Zugarramurdi and Urdax, two Basque villages within the region of Spanish Navarre, on the northern side of the Pyrenees, near the French border.