Hassan Sabbah is a title used by multiple individuals in the Fate/Grand Order series, each serving as the leader of the Hashashin. The name refers to the legendary historical figure known for founding the Nizari Ismaili state and its military group, the Assassins. In Fate/Grand Order, various characters take on the Hassan Sabbah mantle, each with unique abilities and traits. They are typically summoned as Assassin-class Servants and are notable for their role in stealth and espionage, often appearing as formidable opponents or allies in the storyline.