Excerpts from Books and Wikipedia
Pope Sixtus IV was personally involved in Pazzi Conspiracy; "Commissioned the Sistine Chapel. Authorized an Inquisition targeting converted Jewish Christians in Spain at the request of Queen Isabella and King Ferdinand." [Wikipedia]"Isabella of Castile and Ferdinand of Aragon--whose marriage in 1469 had brought together the two kingdoms of medieval Spain--saw it as their divine duty to drive heresy from their lands. Isabella had already obtained the pope's permission to establish the Inquisition in Castile . . . Pope Sixtus IV issued a bull instituting the Inquisition throughout Ferdinand's territories of Aragon. . . . The crown, the Inquisition, and the informers all got a share of the victim's confiscated property. The Inquisition later moved on to target humanists and Protestants, especially during Philip II's reign. This was used as propaganda by Spain's enemies, particularly in England, and it was at this time that the Spanish Inquisition acquired its, possible exaggerated, reputation for sadistic cruelty." [1001 Days] "The Spanish Inquisition was set up to cure the perceived ills created by five hundred years of a society that did tolerate contradictions of all sorts."