Pope Gregory XV, born Alessandro Ludovisi, was the head of the Catholic Church and ruler of the Papal States from 9 February 1621 until his death in 1623. He is notable for founding the Congregation for the Propagation of the Faith, an organization tasked with overseeing the spread of Catholicism and missionary work. Gregory XV was also responsible for the canonization of Saints Ignatius of Loyola, Francis Xavier, Teresa of Ávila, and Philip Neri, which solidified his commitment to the Counter-Reformation.

Pope Paul V, born Camillo Borghese, was head of the Catholic Church and ruler of the Papal States from 16 May 1605 to his death, in January 1621. In 1611, he honored Galileo Galilei as a member of the papal Accademia dei Lincei and supported his discoveries. In 1616, Pope Paul V instructed Cardinal Robert Bellarmine to inform Galileo that the Copernican theory could not be taught as fact, but Bellarmine's certificate allowed Galileo to continue his studies in search for evidence and use the geocentric model as a theoretical device. That same year Paul V assured Galileo that he was safe from persecution so long as he, the Pope, should live. Bellarmine's certificate was used by Galileo for his defense at the trial of 1633.