Pope Pius IV, born Giovanni Angelo Medici, was head of the Catholic Church and ruler of the Papal States from 25 December 1559 to his death in 1565. Born in Milan, his family considered itself a branch of the House of Medici and used the same coat of arms. Although modern historians have found no proof of this connection, the Medici of Florence recognized the claims of the Medici of Milan in the early 16th century.
Pope Paul III appointed Medici Archbishop of Ragusa, and sent him on diplomatic missions to Germany and Hungary. He presided over the final session of the Council of Trent. His nephew, Cardinal Charles Borromeo, was a close adviser. As pope, Pius IV initiated a number of building projects in Rome, including one to improve the water supply.