al-Hassan ibn-al-Sabbah was a Persian Nizārī missionary who converted a community in the late 11th century in the heart of the Alborz Mountains of northern Iran. The place was called Alamut and was attributed to an ancient king of Daylam. He founded a group whose members are sometimes referred to as the Hashshashin or Assassins to protect from attackers outside of Iran.
The Hashashin, also spelled Hashashiyyin or Hashshashin, were a radical sect within the Nizari Ismaili branch of Shi’i Islam. They formed during the 11th century and lasted until the 13th century.
حشاشین is the Arabic spelling of Hashashin.
Etymologies are interesting. Say the word "doubt" aloud. What is that "b" doing there? Does it have any purpose? Gina Cooke explains the long and winding history of "doubt" and why the spelling, though it seems random, is a wink to its storied past.