1. Thomas Cajetan, known as Gaetanus, commonly Tommaso de Vio or Thomas de Vio, was an Italian philosopher, theologian, the Master of the Order of Preachers 1508 to 1518, and cardinal from 1517 until his death.

1. Thomas Cajetan, known as Gaetanus, commonly Tommaso de Vio or Thomas de Vio, was an Italian philosopher, theologian, the Master of the Order of Preachers 1508 to 1518, and cardinal from 1517 until his death.
Thomas Cajetan was a leading theologian of his day who is 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.
Thomas Cajetan is not to be confused with his contemporary Saint Cajetan, the founder of the Theatines.
Thomas Cajetan was born in Gaeta, then part of the Kingdom of Naples, as Jacopo Vio.
The name Tommaso was taken as his religious as a friar, 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 Cajetan Aquinas, becoming before the age of thirty a doctor of theology at Padua, and subsequently professor of metaphysics.
Thomas Cajetan became general procurator in 1507 and general of the Dominicans a year later in 1508.
Thomas Cajetan displayed vigorous support for the papacy in a series of publications.
Jacques Almain answered this work, and Thomas Cajetan replied in his Apologia.
Thomas 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.
Thomas Cajetan resigned Palermo in 1519 to become Bishop of Gaeta, as granted him by the Emperor Charles V for whose election De Vio had laboured zealously.
In 1518, Thomas Cajetan was sent as legate to the Diet of Augsburg and at the behest of the Frederick III, Elector of Saxony was entrusted with examining the teachings of Martin Luther.
In 1519, Thomas Cajetan helped in drawing up the bill of excommunication against Luther.
Thomas Cajetan retained influence under Pope Clement VII, suffered a short term of imprisonment after the storming of Rome by the Constable of Bourbon and by Frundsberg, retired to his diocese for a few years, and, returning to Rome in 1530, assumed his old position of influence with Pope Clement, on whose behalf he drafted the decision rejecting the petition made by Henry VIII of England for the annulment of his marriage to Catharine of Aragon.
Thomas Cajetan wrote opinions on subjects of practical importance, such as the disposition of plundered goods whose ownership could not be determined.
Thomas Cajetan was a man of austere piety and fervent zeal.
Cajetan and his successors therefore, in Gilson's account, represented Thomas as focused on the forms and essences of beings only, and not on the existence of all things as participation in the pure actuality which is God.
De Lubac argued that Thomas Cajetan treated Aquinas as an Aristotelian, working with a definition of nature from Aristotle's Physics, which effectively turned human nature into a reality essentially closed in on itself, with its own intrinsic powers, desires and goals.
In 2006, Ralph McInerny and other scholars challenged the negative assessment of Thomas Cajetan's work made by De Lubac and Gilson.
McInerny writes that the criticisms of Thomas Cajetan are not in fact supported by evidence from his works, and furthermore that it is not Thomas Cajetan but Gilson whose interpretation of Aquinas is a departure from the latter's beliefs.
Notably, Thomas Cajetan revived earlier Christian doubts as to the apostolic authorship of the Epistles of James, Jude, 2 John, and 3 John, as well as opposing Pauline authorship of the Epistle to the Hebrews.