阿泰尔是刺客骑士团的成员，是反对圣殿骑士的一个派系。在第三次十字军东征之前，阿泰尔是整个骑士团中最熟练的刺客。他没能暗杀罗伯特·德·萨布尔（Robert de Sable），并将圣殿骑士团带回马斯亚夫（Masyaf）后被降职。降职后，阿尔泰尔的刺客大师兼领导人思南为他提供了任务。为了恢复以前的声誉，阿尔泰尔被命令杀死散布在阿克，马斯亚夫和耶路撒冷三个城市的七个高级圣殿骑士。Sibrand，Montferrat的William和Garnier de Naplouse在Acre等他。阿泰尔（Altaïr）在Masyaf附近杀害了Vizier Abull Aswad和Tamir Bin Musa，并在耶路撒冷杀害了Maj Aldin，Tallal和Robert de Sable。随着声誉的恢复和任务的完成，阿泰尔见到了他的导师阿尔莫林，却发现阿尔莫林实际上是一个秘密的圣殿骑士，他操纵阿尔泰来消灭阿尔莫林的前盟友以巩固自己的力量。随着阿尔莫林对信条的背叛的启示，阿泰尔被迫面对并杀死了他的前导师。阿尔莫林死后，阿泰尔（Altaïr）从罗伯特·德·萨布尔（Robert de Sable）手中抢夺了他先前掠夺的宝藏：能够改变世界命运的难以捉摸的伊甸碎片。
de WilliamGarnier de NaplouseAcreVizier Abull AswadTamir Bin Maj Robert de Sable de
Altaïr was a member of the Assassin Order, a faction in opposition to the Knights Templar. Before the Third Crusade, Altaïr was the most skilled Assassin in the entire Order. He was demoted after he failed to assassinate Robert de Sable and led the Templars back to Masyaf. After his demotion, Altaïr's master and leader of the Assassins, Sinan, offered him a task. To regain his former reputation, Altaïr was ordered to kill seven high-ranked Templars scattered throughout the three cities of Acre, Masyaf, and Jerusalem. Sibrand, William of Montferrat and Garnier de Naplouse awaited him in Acre. Altaïr killed Vizier Abull Aswad and Tamir Bin Musa near Masyaf, and killed Maj Aldin, Tallal, and Robert de Sable in Jerusalem. With his reputation restored and his missions completed, Altaïr returned to his master Sinan, only to discover that Sinan was in fact secretly a Templar who had manipulated Altaïr to eliminate Sinan's former allies to consolidate more power for himself. With this revelation of Sinan's betrayal of the Creed, Altaïr was forced to confront and kill his former master. With Sinan dead, Altaïr obtained the treasure he had previously looted from Robert de Sable: the elusive Piece of Eden capable of altering the world's fate.