In the original 2007 Assassin's Creed video game, Altaïr belongs to the Assassins.
The game presents Altaïr Ibn-La'Ahad as a senior member of the Assassin Brotherhood during the Third Crusade. His missions take him through cities including Masyaf, Jerusalem, Acre, and Damascus. The Brotherhood operates secretly and opposes the Templars, who seek control through powerful relics and political influence.
The historical Assassins were associated with the Nizari Ismaili state, but the game's fictional Brotherhood is a heavily dramatized interpretation rather than a direct historical recreation. The series uses the Assassin-versus-Templar conflict to connect real medieval settings with science-fiction elements involving genetic memory and the Animus.
A common mix-up is assuming that Altaïr is the first playable Assassin in the entire fictional chronology. Later games depict earlier historical Assassins, while Altaïr remains the protagonist of the first released main entry and an important figure throughout the wider series.