Which Assassin's Creed game first introduced the playable character Desmond Miles?

Assassin's Creed first introduced the playable character Desmond Miles.

Desmond is the modern-day protagonist of the original 2007 game. Abducted by Abstergo Industries, he is forced to use the Animus, a machine that allows him to relive genetic memories of his ancestors. The first game connects Desmond's present-day captivity with Altaïr Ibn-La'Ahad's life during the Third Crusade.

Although much of the player's time is spent controlling Altaïr, Desmond is playable in short modern sections and provides the framework for the historical missions. His modern-day storyline continues through Assassin's Creed II, Brotherhood, Revelations, and Assassin's Creed III.

Some people identify Assassin's Creed II as Desmond's introduction because it expands his role considerably. However, the character and the Animus-based narrative structure both appear in the 2007 original, making that game his first appearance.