Which real-world organization inspired the Assassin Brotherhood in Assassin's Creed?

The Nizari Ismailis inspired the Assassin Brotherhood in Assassin's Creed.

The series' fictional Assassins draw substantially on the medieval Nizari Ismaili community, a branch of Shia Islam that established strongholds in parts of Persia and Syria. Their best-known fortress was Alamut in present-day Iran. Medieval sources and later European traditions associated the group with targeted political killings, helping create the historical background for the game's Assassin mythology.

Assassin's Creed transforms this history into a global secret order dedicated to free will and opposed to Templar control. The fictional Brotherhood, its creed, costumes, and centuries-spanning conspiracy are not literal portrayals of Nizari Ismaili history. The term “Hashshashin” is also a later and contested label, so it should not be treated as a complete historical description of the community. The Knights Templar are the Assassins' fictional ideological rivals, not their inspiration.