In the first Assassin's Creed game, Altaïr Ibn-La'Ahad operates during the Third Crusade.
The game is set mainly in the year 1191, when the Third Crusade was being fought in the Holy Land. Altaïr travels among cities including Jerusalem, Acre, and Damascus while pursuing targets connected to the Templars. The story places fictional Assassin characters alongside historical leaders and political forces of the period.
The Third Crusade lasted from 1189 to 1192. It followed the Muslim ruler Saladin's capture of Jerusalem in 1187 and involved European rulers such as Richard I of England. Assassin's Creed uses this historical framework for its fictional conflict rather than presenting a complete historical account.
Altaïr is not the same character as Ezio Auditore, who stars in Assassin's Creed II and lives during the Italian Renaissance. The first game also established the series' recurring use of a modern-day framework, in which Desmond Miles accesses ancestral memories through the Animus.