Born to an Assassin family of a Muslim father, Umar and a Christian mother, Maud, Altair was raised to become an Assassin since birth. Altaïr became a Master Assassin at the age of twenty five, the youngest to obtain the rank by that time. Due to his arrogance and recklessness at the time, he failed to acquire an Apple of Eden from Robert de Sablé in July of 1191 which subsequently led the Templars to attacking Masyaf, the headquarters of the Assassin Brotherhood in present day Syria. Despite helping the other Assassins to fend off the attack, he was demoted to the rank of novice.

In order to reclaim his honor and rank, Altaïr was tasked with the assassination of nine targets who, unbeknownst to him, made up the ranks of the Templar Order in the Holy Land, Altaïr began a quest to change his methods and free the Kingdom from corruption. During his quest, Altaïr learned of a conspiracy far more sinister than he originally believed, involving a millennia old opposing faction, the corruption and power hunger of his own mentor, and an ancient technology comparable to magic. Upon completing his quest, he cleansed the Assassin Brotherhood of its treacherous leader, Al Mualim. 

In the aftermath, Altaïr became Mentor, taking the Assassin Brotherhood into a more secretive direction.

With the Apple of Eden and its vast knowledge in his possession, Altaïr made several discoveries and inventions that greatly helped the Assassin’s presence and progression throughout the coming centuries. He changed the way members of his Order lived their lives, writing the details in his codex for later generations of the Order to derive wisdom from. Altaïr’s vision of the Assassin Order was for them to be spread across the world, living among the people, hidden in plain sight. He began establishing numerous Guilds for the Assassins around the globe. Throughout his travels, he strengthened his Creed’s presence, stopping various Templar conspiracies as well as halting the incessant invasion of Genghis Khan.

During his tenure as Mentor, with the Apple of Eden and the vast knowledge stored within it at hand, Altaïr His leadership saw to the spread of the Assassins’ influence across the Old World. Altaïr is an ancestor of Desmond Miles, through his maternal bloodline.