Leo X (1475-1521), a pope from 1513-21, was among the most extravagant of Renaissance popes. Originally named Giovanni de' Medici, son of Lorenzo de' Medici, he was born in Florence on December 11, 1475. He was made a cardinal deacon at the age of 13 and elected pope at 37. He was an able administrator and skillful in politics and foreign affairs. He succeeded in driving the invading French out of Italy but in 1515 was defeated by Francis I, king of France. In 1516 the relations of the papacy with France were settled through a concordat, whereby the independence of the Gallican church (sometimes referred to as Gallicanism) was ended. The king, however, received the power to name bishops and other high church officials, who were then assured of appointment despite the pope's theoretical power of veto. By Leo's efforts, the papacy became the dominant political force in Italy. The Fifth Lateran Council was concluded (1517) in Leo's pontificate; among its actions were ratification of the concordat with France and the establishment of a system of book censorship.

Leo was brought up in the Medici tradition of scholarship and appreciation of arts and letters, and his fame rests more on his role as a patron of the arts than as an ecclesiastical figure. He spent huge sums on projects carried out by such masters as Raphael and Bramante. His extravagances as a patron of arts, as in the rebuilding of Saint Peter's Basilica, and the pomp of his court were indirectly responsible for the Reformation movement. The sale of indulgences by the German monk Johann Tetzel and the indignant response of Martin Luther in 1517 set in motion the upheaval that created Protestantism. Leo condemned the Lutheran heresies and excommunicated Luther and his followers in 1520. Leo died on December 1, 1521, in Rome.