Hasan-i Sabbah, also known as Hasan I of Alamut, was a religious and military leader, founder of the Nizari Ismai'li sect widely known as the Hashshashin or the Order of Assassins, as well as the Nizari Ismaili state, ruling from 1090 to 1124 AD.

Alamut is a mountain fortress at an altitude of 2163 meters at the central Alborz, in the Iranian stanza of Qazvin, about 100 kilometers from Tehran. In 1090 AD, the Alamut Castle, a mountain fortress in present-day Iran, came into the possession of Hassan-i Sabbah, a champion of the Nizari Ismaili cause. Until 1256, Alamut functioned as the headquarters of the Nizari Ismaili state, which included a series of strategic strongholds scattered throughout Persia and Syria, with each stronghold being surrounded by swathes of hostile territory.