In Assassin's Creed Brotherhood, which Borgia family member is Ezio's main enemy?

In Assassin's Creed Brotherhood, Ezio's main enemy is Cesare Borgia.

Cesare is the military leader of the Borgia family and the central antagonist of Brotherhood. After the events of Assassin's Creed II, he expands Borgia power in Italy and uses Rome as the base of his political and military ambitions. Ezio works to weaken that power by rebuilding the Assassin Brotherhood and liberating districts of the city.

Rodrigo Borgia, known in the game as Pope Alexander VI, is also a major figure from the previous title and remains part of the family conflict. However, Brotherhood places Cesare at the center of Ezio's direct struggle.

The historical Cesare Borgia was a Renaissance Italian nobleman and military commander. The game dramatizes his relationship with Ezio and incorporates him into the series' fictional Assassin-Templar mythology.