In the original Assassin's Creed (2007), what is the name of the playable Assassin?

The playable Assassin in the original Assassin's Creed (2007) is Altaïr Ibn-La'Ahad.

Altaïr is a Syrian Assassin operating during the Third Crusade, with the game’s main story set in 1191. The player follows his missions across cities including Masyaf, Damascus, Acre, and Jerusalem. His name is sometimes written with different apostrophe or transliteration styles, but “Altaïr Ibn-La'Ahad” is the standard English form used for the character.

Altaïr begins the game as a highly ranked Assassin whose reckless actions lead to punishment and a loss of status. His recovery becomes the framework for the investigation into nine targets and the wider conflict between Assassins and Templars. Ezio Auditore, the better-known protagonist of later games, does not appear as the player character in this first title.