Cesare Borgia is Ezio Auditore's principal enemy in Assassin's Creed: Brotherhood.
The game follows Ezio in Rome, where Cesare Borgia commands a powerful military and political network. Cesare is the son of Rodrigo Borgia, who became Pope Alexander VI in 1492. Although Rodrigo is a major antagonist in Assassin's Creed II, Brotherhood shifts the central confrontation toward Cesare and his campaign to dominate Italy.
The historical Cesare Borgia was a Renaissance cardinal, military leader, and politician. The game draws on those real-world roles but places him inside its fictional struggle between Assassins and Templars. Ezio works with a rebuilt Brotherhood and Roman allies to weaken Cesare's influence.
A frequent mix-up is answering Rodrigo Borgia because he is the major Borgia villain in the previous game. In Brotherhood, Cesare is the named principal foe, while Rodrigo remains an important connected figure.