Altaïr's surname in the first Assassin's Creed is Ibn-La'Ahad.
Altaïr Ibn-La'Ahad is a Syrian Assassin who serves as the protagonist of the original game. His name is commonly translated as “son of no one,” reflecting the character's orphaned background and the Arabic naming tradition used for him.
The first game is set during the Third Crusade, primarily in the cities of Masyaf, Acre, Damascus, and Jerusalem. After Altaïr fails a mission, his rank and equipment are reduced; he must then complete assignments and regain the trust of his mentor, Al Mualim.
Players sometimes remember Altaïr only by his first name, or confuse his surname with those of later protagonists such as Ezio Auditore and Edward Kenway. “Ibn-La'Ahad” is the distinctive family name attached to Altaïr in official game materials and reference works.