Cesare Borgia (Spanish: César Borja; 13 September 1475 – 12 March 1507) was an Italian politician and condottiero whose fight for power was a major inspiration for "The Prince" by Machiavelli. He was an illegitimate son of Pope Alexander VI and member of the Spanish-Aragonese House of Borgia. After initially entering the church and becoming a cardinal on his father's election to the Papacy, he became, after the death of his brother in 1498, the first person to resign a cardinalate. He served as a condottiero for the King of France Louis XII around 1500 and occupied Milan and Naples during the Italian Wars. At the same time he carved out a state for himself in Central Italy, but after his father's death he was unable to retain power for long. According to Machiavelli, this was not due to a lack of foresight, but his error in creating a new pope. Like many aspects of Cesare Borgia's life, the date of his birth is a subject of dispute. He was born in Subiaco in either 1475 or 1476—the illegitimate son of Cardinal Roderic Llançol i de Borja, usually known as "Rodrigo Borgia", later Pope Alexander VI, and his Italian mistress Vannozza dei Cattanei, about whom information is sparse. The Borgia family originally came from the Kingdom of Valencia, and rose to prominence during the mid-15th century; Cesare's great-uncle Alphonso Borgia (1378–1458), bishop of Valencia, was elected Pope Callixtus III in 1455. Cesare's father, Pope Alexander VI, was the first pope who openly recognized his children born out of wedlock. Stefano Infessura writes that Cardinal Borgia falsely claimed Cesare to be the legitimate son of another man—Domenico d'Arignano, the nominal husband of Vannozza dei Cattanei. More likely, Pope Sixtus IV granted Cesare a release from the necessity of proving his birth in a papal bull of 1 October 1480. Cesare was initially groomed for a career in the Church. Following school in Perugia and Pisa, Cesare studied law at the Studium Urbis (nowadays Sapienza University of Rome). He was made Bishop of Pamplona at the age of 15 and archbishop of Valencia at 17. In 1493, he had also been appointed bishop of both Castres and Elne. In 1494, he also received the title of abbot of the abbey of Saint-Michel-de-Cuxa. Along with his father's elevation to Pope, Cesare was made Cardinal at the age of 18. Alexander VI staked the hopes of the Borgia family on Cesare's brother Giovanni, who was made captain general of the military forces of the papacy. Giovanni was assassinated in 1497 under mysterious circumstances. Several contemporaries suggested that Cesare might have been his killer, as Giovanni's disappearance could finally open to him a long-awaited military career and also solve the jealousy over Sancha of Aragon, wife of Cesare's younger brother, Gioffre, and mistress of both Cesare and Giovanni. Cesare's role in the act has never been clear. However, he had no definitive motive, as he was likely to be given a powerful secular position, whether or not his brother lived. It is possible that Giovanni was killed as a result of a sexual liaison. On 17 August 1498, Cesare became the first person in history to resign the cardinalate, which he did in order to pursue a military career. On the same day, Louis XII of France named Cesare Duke of Valentinois, and this title, along with his former position as Cardinal of Valencia, explains the nickname "Valentino".

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