In the original Assassin's Creed, Masyaf is home to Altaïr Ibn-La'Ahad at the start of the game.
Masyaf is a mountain settlement in modern-day Syria and serves as the headquarters of the Assassin Brotherhood during the game's 1191 storyline. Altaïr returns there after missions and receives orders from Al Mualim, the Brotherhood's leader. The location also provides the game's main training and narrative hub.
The game's historical cities—Acre, Damascus, and Jerusalem—are important mission locations, but none is Altaïr's home base. Masyaf is fictionalized for the game while drawing on the historical association between the region and the medieval Nizari Ismaili community. The settlement's fortress and mountainous setting help establish the Assassins' secluded organization.
Later Assassin's Creed stories revisit Masyaf and connect it with other eras of the Brotherhood. It is therefore both a recognizable setting and a key part of the series' recurring historical mythology.