The Assassins is the name used to refer to the medieval Nizari Ismailis, particularly those of Persia and Syria, by Westerners. Often characterized as a secret order of assassins led by a mysterious “Old Man of the Mountain,” the Nizari Ismailis were an Islamic sect that formed in the late 11th century from a split within Ismailism, itself a branch of Shia Islam. In time, the Nizaris began to pose a military threat to Sunni Seljuq authority within the Persian territories by capturing and inhabiting several mountain fortresses under the leadership of Hassan-i Sabbah, who is typically regarded as the founder of the Assassins.
Hassan was himself a member of the Order of the Black Star who had broken off from the Secret Society when he became more concerned about the geopolitics of the region than trying to become the sole occult power in the land. The Assassins directed their occult knowledge to enhance their abilities as dangerous and highly skilled killers. Although they spent much of their time targeting Christians, they would never pass up an opportunity to eliminate a Nephilim.