Ezio Auditore is the Assassin Brotherhood's mentor in Assassin's Creed Revelations.
Revelations presents Ezio in his later years, after the events of Assassin's Creed II and Brotherhood. He travels to Constantinople in search of Masyaf keys connected with Altaïr Ibn-La'Ahad's legacy. By this point, Ezio is not a newly recruited Assassin; he is an experienced leader and mentor guiding the Brotherhood.
Altaïr is central to the game's historical storyline and appears through memories unlocked by the Masyaf keys. His importance can make him seem like the answer, but Revelations specifically follows Ezio as the playable protagonist and mentor. Connor Kenway belongs to Assassin's Creed III, while Arno Dorian stars in Unity.
Revelations was released in 2011 and completed Ezio's main trilogy. Its setting, Constantinople, is historically situated in the early sixteenth century under Ottoman rule. The game also links Ezio and Altaïr, two protagonists from different generations of the fictional Assassin tradition.