he Assassins were an order of Nizari Ismailis, particularly those of Persia and Syria that formed in the late 11th century. In time, the order began to pose a strong military threat to Sunni Seljuq authority within the Persian territories by capturing and inhabiting many mountain fortresses under the leadership of Hassan-i Sabbah.

The name "Assassin" is often said to derive from the Arabic Hashishin or "users of hashish， thought to have been originally derogatory and used by their adversaries during the Middle Ages. In actuality, the word is a misnomer for the Nizari Ismailis applied abusively to them by the Mustali Ismailis during the fall of the decaying Ismaili Fatimid Empire when the two streams separated from each other. In 1122 the Mustalian dynasty Fatimid caliph al-Amir referred to the Nizaris as the hashishiyya "without any explanation" and "without actually accusing them of using hashish, a product of hemp"，
The term hashishiyya or hashishi as used by Muslim sources is used metaphorically in its abusive sense (i.e. "irreligious social outcasts", "low-class rabble", etc.), while "the literal interpretation of this term in referring to the Nizaris (as hashish consuming intoxicated assassins) is rooted in the fantasies of medieval Westerners and their imaginative ignorance of Islam and the Ismailis，
Mentions of Assassins were preserved within European sources such as the writings of Marco Polo, where they are depicted as trained killers, responsible for the systematic elimination of opposing figures.