In Assassin's Creed, Altaïr Ibn-La'Ahad's mentor in the Masyaf Brotherhood is Al Mualim.
Al Mualim is the Brotherhood's elderly leader at the beginning of the first Assassin's Creed game. He oversees the fortress at Masyaf and sends Altaïr on missions against important figures during the Third Crusade. After Altaïr breaks the Brotherhood's code during a mission, Al Mualim strips him of his rank and equipment before assigning him a series of assassination contracts.
The name is an Arabic honorific meaning “the teacher” or “the master,” rather than a personal name used in the same way as Altaïr's. The character's historical inspiration is connected to Rashid ad-Din Sinan, a real leader of the Nizari Ismaili state, though the game's story freely fictionalizes him.
A common mix-up is confusing Al Mualim with the later Assassin leader Abbas Sofian, who appears in Assassin's Creed: Revelations and has a different relationship with Altaïr.