Pius IV was born Giovanni Angelo Medici in Milan in 1499. Trained in law, he advanced through a series of ecclesiastical and administrative offices before becoming a cardinal. Despite his surname, he did not belong to the famous Florentine Medici dynasty. In December 1559 he was elected pope, succeeding the severe Paul IV.
His most important achievement was the resumption and completion of the Council of Trent. Meeting intermittently since 1545, the council had sought to address Protestant challenges and problems within the Catholic Church itself. Under Pius IV its final sessions ended in 1563, and he subsequently confirmed its decisions on doctrine, discipline and reform.
In several respects Pius IV adopted a less severe approach than his predecessor, although he remained determined to preserve Catholic unity. He relied heavily on his nephew Carlo Borromeo, later renowned as a reforming archbishop. In 1564 the pope promulgated a revised Index of Forbidden Books, less restrictive than the 1559 version. Pius IV died in Rome in 1565. His pontificate marked a turning point: the decrees of Trent became the foundation for Catholic renewal over the following centuries.
