Desmond Miles is the modern-day protagonist controlled by players in the first Assassin's Creed.
Desmond is a former Assassin who has been captured by Abstergo Industries and forced to use the Animus. The device allows him to relive genetic memories belonging to his ancestor Altaïr Ibn-La'Ahad. In the modern-day sections, Desmond learns about the Assassins, the Templars, and Abstergo while searching for a way to escape.
Altaïr is the historical protagonist, so the two roles are easy to confuse. William Miles is Desmond's father and a later Assassin leader, while Warren Vidic is an Abstergo scientist overseeing the Animus project. Clay Kaczmarek is another Animus subject introduced in later games. Desmond remains the modern-day lead across several early mainline installments before the series changes its modern protagonist structure.