Who was pope before Gregory XIII?
Pope Gregory XIII
Upon the death of Pope Pius V (1566–1572), the conclave chose Cardinal Boncompagni, who assumed the name of Gregory XIII in homage to the great reforming Pope, Gregory I (590–604), surnamed the Great. It was a very brief conclave, lasting less than 24 hours. Many historians have attributed this to the influence and backing of the Spanish King. Cardinal Borromeo and the cardinals wishing reform accepted Boncompagni's candidature and so supported him in the conclave while the Spanish faction also deemed him acceptable due to his success as a nuncio in Spain.
Pope John XIII
John XIII died on September 6, 972, and was buried in the Basilica of Saint Paul Outside the Walls. He was succeeded by Pope Benedict VI. It was during John's reign that earliest surviving written mention of the ancient practice of the blessing of church bells comes from.