Ezio Auditore da Firenze serves as the Mentor of the Italian Brotherhood in Assassin's Creed: Brotherhood.
The game continues Ezio's story after Assassin's Creed II and places him primarily in Rome, where the Borgia family controls much of the city. Ezio rebuilds the local Brotherhood, recruits new Assassins, and works to weaken Borgia power.
By this stage, Ezio is no longer merely learning the Assassin way. He acts as a leader responsible for training recruits, coordinating missions, and restoring the organization in Italy. The game also expands the series with a larger recruitable Brotherhood and a major multiplayer mode.
Mario Auditore is Ezio's uncle and an earlier mentor, while Niccolò Machiavelli advises Ezio. Their roles explain why they are sometimes mistaken for the Brotherhood's central leader in the game.