Assassin's Creed Revelations follows both Ezio Auditore and Altaïr Ibn-La'Ahad. Ezio is the game's playable historical protagonist, while Altaïr's life is explored through memory sequences connected to the Masyaf Keys.
Ezio travels to Constantinople in the early sixteenth century while searching for the keys to Altaïr's library in Masyaf. His investigation brings him into conflict with Byzantine Templars and connects his story to the earlier Assassin leader's legacy.
Altaïr's sections show important stages of his life after the events of the original Assassin's Creed. The game therefore serves as a conclusion to Altaïr's arc and the final major chapter of Ezio's personal story. The modern-day plot continues to feature Desmond Miles.
The pairing is specific to Revelations: Ezio and Altaïr do not simply appear as unrelated cameos. Their narratives are deliberately linked through the library, the memory keys, and the long history of the Assassin Brotherhood.