Pope Julius II (Latin: Iulius II; Italian: Giulio II; born Giuliano della Rovere; 5 December 1443 – 21 February 1513) was head of the Catholic Church and ruler of the Papal States from 1503 to his death, in February 1513. Nicknamed the Warrior Pope, the Battle Pope or the Fearsome Pope, it is often speculated that he had chosen his papal name not in honor of Pope Julius I but in emulation of Julius Caesar. One of the most powerful and influential popes, Julius II was a central figure of the High Renaissance and left a significant cultural and political legacy. As a result of his policies during the Italian Wars, the Papal States increased their power and centralization, and the office of the papacy continued to be crucial, diplomatically and politically, during the entirety of the 16th century in Italy and Europe.

In 1506, Julius II established the Vatican Museums and initiated the rebuilding of the St. Peter's Basilica. The same year he organized the famous Swiss Guard for his personal protection and commanded a successful campaign in Romagna against local lords. The interests of Julius II lay also in the New World, as he ratified the Treaty of Tordesillas, establishing the first bishoprics in the Americas and beginning the Catholicization of Latin America. In 1508, he commissioned the Raphael Rooms and Michelangelo's paintings in the Sistine Chapel.

Pope Julius II allowed people seeking indulgences to donate money to the Church, which would be used for the construction of Saint Peter's Basilica. He was fiercely satirized after his death by Erasmus of Rotterdam in Julius Excluded from Heaven, in which the drunken pope, denied entry to heaven by St. Peter, justifies his worldly life and plots to create a rival abode from which to conquer heaven.

Julius II became pope in the context of the Italian Wars, a period in which the major powers of Europe fought for primacy in the Italian Peninsula. Louis XII of France controlled the Duchy of Milan, previously held by the Sforzas, and French influence had replaced that of the Medici in the Republic of Florence. The Kingdom of Naples was under Spanish rule. Maximilian I of Austria was hostile to France and Venice, and desired to descend into Italy in order to be crowned Holy Roman Emperor by the pope. The conclave capitulation preceding his election included several terms, such as the opening of an ecumenical council and the organization of a crusade against the Ottoman Turks. Once crowned, Julius II proclaimed instead his goal to centralize the Papal States (in large part a patchwork of communes and signorie) and "free Italy from the barbarians".

In his early years as pope, Julius II targeted the members of the House of Borgia (the Spanish family of the previous Pope, Alexander VI), exiling them or destroying their influence. Cesare Borgia, Duke of Romagna, shared the same fate and lost his possessions.

He joined an anti-Venetian League of Cambrai, formed in December 1508, with the goal of capturing the coast of Romagna from the Venetian Republic. Having achieved this goal during the early stages of the War of the League of Cambrai, he reconciled with Venice (1510), and formed the Holy League (1511) in order to eliminate the French presence in Italy. His main goal was now again to "expel the barbarians" (Fuori i Barbari!). Julius II brought king Ferdinand II of Aragon into the alliance, declaring Naples a papal fief and promising a formal investiture.

Having previously declared that the imperial election was sufficient for Maximilian to style himself as Holy Roman Emperor, he succeeded in distancing the emperor from the king of France. Julius II personally led the papal armed forces at the victorious Siege of Mirandola and, despite subsequent defeats and great losses at the Battle of Ravenna, he ultimately forced the French troops of Louis XII to retreat behind the Alps after the arrival of Swiss mercenaries from the Holy Roman Empire.

At the Congress of Mantua in 1512, Julius II ordered the restoration of Italian families to power in the vacuum of French rule: the Imperial Swiss led by Massimiliano Sforza restored Sforza rule in Milan, and a Spanish army led by Giovanni de Medici restored Medici rule in Florence. The Venetians regained their territories lost to France, and the Papal States annexed Parma and Modena. The conciliarist movement promoted by foreign monarchs was crushed, and Julius II affirmed ultramontanism at the Fifth Lateran Council. This is often presented in traditional historiography as the moment in which Renaissance Italy came the closest to unification after the end of the Italic League of the 15th century. However, Julius II was far away from the possibility to form a single Italian kingdom, if that was his goal at all, since foreign armies were largely involved in his wars and the French were preparing new campaigns against the Swiss for Milan. Naples, even if recognized as a papal fief, was still under Aragon and in fact Julius II was planning to end Spanish presence in the south. Nevertheless, by the end of his pontificate, the papal objective to make the Church the main force in the Italian Wars was achieved. At the Roman Carnival of 1513, Julius II presented himself as the "liberator of Italy".