Hasan-i Sabbah

Hasan al-Sabbah also known as Hasan I of Alamut, was an Iranian religious and military leader, founder of the Nizari Ismai'li sect widely known as the Hashshashin or the Order of Assassins, as well as the Nizari Ismaili state, ruling from 1090 to 1124 AD.

Alongside his role as a formidable leader, Sabbah was an accomplished scholar of mathematics, most notably in geometry, as well as astronomy and philosophy, especially in epistemology. It is narrated that Hasan and the Persian polymath Omar Khayyam were close friends since their student years. He and each of the later Assassin leaders came to be known in the West as the Old Man of the Mountain, a name given to the sect's leader in the writings of Marco Polo that referenced the sect's possession of the commanding mountain fortress of Alamut Castle.