Thomas Cajetan ( ; 20 February 14699 August 1534), also known as Gaetanus, commonly Tommaso de Vio or Thomas de Vio, was an Italian philosopher, theologian, cardinal (from 1517 until his death) and the Master of the Order of Preachers 1508 to 1518. He was a leading theologian of his day who is now best known as the spokesman for Catholic opposition to the teachings of Martin Luther and the Protestant Reformation while he was the Pope's Legate in Augsburg, and among Catholics for his extensive commentary on the Summa Theologica of Thomas Aquinas. He is not to be confused with his contemporary, Saint Cajetan, the founder of the Theatines. Life De Vio was born in Gaeta, then part of the Kingdom of Naples, as Jacopo Vio. The name Tommaso was taken as a monastic name, while the surname Cajetan derives from his native city. At the age of fifteen he entered the Dominican order and devoted himself to the study of the philosophy of St. Thomas Aquinas, becoming before the age of thirty a doctor of theology at Padua, and subsequently professor of metaphysics. A public disputation at Ferrara (1494) with Pico della Mirandola made his reputation as a theologian. He became general procurator in 1507 and general of the Dominicans a year later in 1508. For his zeal in defending the papal rights against the 1511 Council of Pisa, in a series of works which were condemned by the Sorbonne and publicly burnt by order of King Louis XII, he obtained the bishopric of Gaeta, and in 1517 Pope Leo X made him a cardinal and archbishop of Palermo. He appears in 1511 as a supporter of the pope against the claims of the Council of Pisa (1511–1512), called by dissident cardinals to punish Pope Julius II, who had ignored the electoral capitulations he had accepted before being elected. Cajetan composed in defense of his position the Tractatus de Comparatione auctoritatis Papæ et conciliorum ad invicem. Jacques Almain answered this work, and Cajetan replied in his Apologia. Cajetan refused to accept Almain's argument that the Church's polity had to be similar to a lay regime, complete with limits on the ruler. At the Fifth Lateran Council (1512–17) which Pope Julius II set up in opposition to that of Pisa, De Vio played the leading role. During the second session of the council, in which he gave the opening