Altaïr Ibn-La'ahad, a distant ancestor of Desmond Miles, brought crucial reforms to the Assassin Brotherhood and expanded its influence beyond its Middle Eastern origins.

Altaïr was skilled but arrogant, the youngest man ever to gain the rank of Master. On a mission to retrieve an artifact called the Apple of Eden, he broke the three tenets of the Assassin's Creed, costing him his status. His task for redemption was to stop the Templars, who were playing the Crusaders and Saracens against one another for control of the Holy Land. Altaïr eventually earned the respect of King Richard, hastening the end of the Third Crusade.

The wisdom Altaïr gained let him uncover that his mentor, Al Mualim, was a traitor using the Apple's unfathomable powers for his own selfish desires. After restoring order, he became the Mentor, started a family, and reformed Assassin practices.

Altaïr dedicated the rest of his life to creating a Codex containing his memories, together with the information extracted from the Apple, in the hopes that future generations would use it to establish Assassin guilds throughout the world.