Hassan-e Sabbah was the founder of the infamous sect known in medieval times as the “Assassins”. Although Sabbah was a Persian Ismailite Shia, when the Shia caliph in Cairo died in 1094, Sabbah and others refused to acknowledge the new caliph, and instead followed the dead caliph’s eldest son, Nizar. This breakaway sect became known as the Nizari Ismailites, and made a reputation for itself by implacable hostility to the Shia caliph in Cairo and the Sunni caliph in Baghdad.

Hassan’s rejection of the new caliph made him a wanted man, and he went into hiding, eventually seizing control of the Alamut fortress in the rocky Alborz mountains north-west of Tehran and 60 miles from the Caspian shore. From there, he set up a network of Nizari Ismailite strongholds all over modern-day Iran and Iraq.