Cesare Borgia (September, 1475 - March 12, 1507), Duke of Valencia, the illegitimate son of Pope Alexander VI (Rodrigo Borgia) and brother to Lucrezia Borgia.

Cesare was born to the mistress of Rodrigo Borgia, an important cardinal and nephew of Pope Calixtus III. Borgia planned to use the forces of the papacy to further his own family. After years of scheming, Rodrigo had himself elected Pope in 1492.

Cesare was initially groomed by his father for a Church career and was elevated by his father to the rank of Cardinal by the age of 22. Alexander VI staked the hopes for the Borgia family on Cesare's brother Juan, who was made captain general of the military forces of the papacy. When Juan was assassinated, Alexander was forced to substitute Cesare, despite the fact that this conflicted with Cesare's vows.

Cesare's career was founded entirely upon his father's ability to distribute patronage. Appointed commander of the papal armies, Cesare was sent by his father to subdue the cities of Romagna in central Italy. Though in theory subject directly to the pope, the rulers of these cities had been practically independent or dependent on other states for generations. Alexander VI hoped that by subduing them his son would create a new central Italian kingdom that would rival Naples, Florence, Milan and Venice.

Cesare Borgia briefly employed Leonardo da Vinci as military architect and engineer at one point. Da Vinci had worked at the Milanese court of Ludovico Sforza for many years, until Charles VIII of France drove Sforza out of Italy.

Though an immensely capable general and statesman, Cesare could do nothing without continued papal patronage. The death of his father ended his own career. Gravely ill at the time that his father died in 1503, his political enemies, led by Pope Julius II, were able to seize and imprison him. Exiled to Spain, in 1504, he escaped from a Spanish prison two years later and joined his brother-in-law, King Jean d'Albret of Navarre . Serving Navarre as a soldier, he died at the siege of Viana in 1507, at the age of thirty-one.

Cesare Borgia was greatly admired by Niccolo Machiavelli, who knew him personally. Machiavelli used many of his exploits and tactics as examples in The Prince. A few scholars, however, have argued that Machiavelli's praise for Borgia was a parody, to cover up the actual anti-hero of the work, Ferdinand II of Aragon.

Notable fictionalized films about Cesare Borgia include:

• Lucrezia Borgia (Richard Oswald , 1926), a silent movie starring Liane Haid and Conrad Veidt
• The Black Duke (1961) starring Cameron Mitchell and Gloria Milland .
• Bride of Vengeance (1948) starring Macdonald Carey and Paulette Goddard.
• Prince of Foxes (1949) starring Orson Welles and Tyrone Power (from the best-selling book by Samuel Shellabarger).