The Animus user played by the player in Assassin's Creed Revelations is Desmond Miles. In the modern-day storyline, Desmond enters the Animus to experience the memories of his ancestor Ezio Auditore and avoid a dangerous mental collapse.
Desmond is the central modern protagonist of the first five main Assassin's Creed games. His genetic connection allows the Animus to access memories belonging to several ancestors, including Altaïr Ibn-La'Ahad, Ezio, and Ratonhnhaké:ton.
Revelations uses a special Animus-related setting called the Black Room during parts of Desmond's recovery. The game also concludes Ezio's personal journey and presents connections between Ezio and Altaïr.
William Miles is Desmond's father and an important Assassin leader, but he is not the playable Animus user in Revelations. Clay Kaczmarek is another modern subject connected to Animus experiments, while Warren Vidic is an Abstergo scientist.