Hasan-i-Sabbah was a Persian Twelver who converted to Ismailism and became an enthusiastic missionary for its cause, and a supporter of Nizar. In his youth he studied alongside the future tentmaker, astronomer and poet Omar Khayyám, and the future prime minister of Persia, Nizam ul-Mulk, whom he later had murdered. In 1090 he took control of Alamut (Eagle’s Nest), a Sunni fortress in the mountains of northern Persia, and established it as the centre of his operations.
Hasan’s followers were named Assassins by the Christian Crusaders who encountered them. They were utterly dedicated to Hasan – sometimes known as the Old Man of the Mountains – and would kill or die on his order. […]
The mythic basis of this unquestioning loyalty is that Hasan had a beautiful garden in a hidden fertile valley in the mountains. The valley ran with streams of milk, honey, wine and pure water; its trees were heavy with fruit. Initiates were drugged, then taken to the valley, where for a few days they lived among its delights, which included palaces, musicians, singers, dancers and houris. Drugged again, they were returned ti Hasan, and were told they gad been given a glimpse of Paradise. If they swore an oath of absolute obedience to Hasan they would return there on their deaths.
[…]
Hasan was a brilliant and ruthless ruler. He took advantage of the political chaos in Persia – he probably helped cause most of it – and he eliminated potential rivals. Within a very short time he had more real power than the supposed rulers, and was feared by Muslims and Christians alike.
Hasan died in 1124, aged 90, having ruled through the fanatical devotion of his followers for nearly 35 years. His successors continued the tradition, having major political and religious figures killed […]. One very successful technique they used was to plant ‘sleepers’ in the Courts of rulers. They would not reveal themselves for years, even decades, until they received a signal, at which point they would kill the completely unsuspecting ruler.
[…]
The Assasins are important to the current narrative for several reasons. They were a powerful, self-sustaining Order with several levels of initiation, oaths of obedience, and secret signs. Their beliefs varied from those of standard Islam, having something in common with Gnostic ideas. Among their beliefs were the teachings that heaven and hell were the same, and that no acts were sinful in themselves because the only good and evil were in obeying or disobeying the imam.
The Assassins are believed by some to have influenced the Knights Templar in a number of ways. […]
– A Brief History of Secret Societies: An Unbiased History of Our Desire for Secret Knowledge (1997), pp. 35-8