In Assassin's Creed, which assassin does Desmond Miles experience through the Animus?

In Assassin's Creed, Desmond Miles experiences the memories of Altaïr Ibn-La'Ahad through the Animus.

Altaïr is the playable assassin in the first game, where his story takes place largely in the Levant during the Third Crusade. He begins as a highly ranked Assassin whose recklessness causes him to lose his status and equipment. His mentor, Al Mualim, then assigns him missions that gradually restore his rank.

Desmond is a modern descendant of Altaïr. Abstergo Industries abducts him and uses the Animus to explore his genetic memories. Although Desmond does not physically become Altaïr, the machine allows him to see and control events from Altaïr's life.

Altaïr's name is often written with different transliteration marks, including Altaïr Ibn-La'Ahad and Altaïr Ibn-La-Ahad. The character later appears in expanded franchise stories, but the original game is the central source of his introduction.