[2][3][4] 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.

[8][9] Hasan is thought to have written an autobiography, which did not survive but seems to underlie the first part of an anonymous Isma'ili biography entitled Sargozasht-e Seyyednā (Persian: سرگذشت سیدنا).

[11] The possibly autobiographical information found in Sargozasht-i Seyyednā is the main source for Hasan's background and early life.

It was in this religious centre that Hasan developed a keen interest in metaphysical matters and adhered to the Twelver code of instruction.

[15] The Ismā'īlī mission worked on three layers: the lowest was the fida'i or foot soldier, followed by the rafīk or comrade, and finally the dā‘ī or missionary.

[3] Hasan's austere and devoted commitment to the da'wa brought him in audience with the chief missionary of the region: 'Abdu l-Malik ibn Attash.

Ibn Attash, suitably impressed with the young seventeen-year-old Hasan, made him Deputy Missionary and advised him to go to Cairo to further his studies.

Some historians have postulated that Hasan, following his conversion, was playing host to some members of the Fatimid caliphate, and this was leaked to the anti-Fatimid and anti-Shī‘a vizier Nizam al-Mulk.

Records exist, some in the fragmentary remains of his autobiography, and from another biography written by Rashid-al-Din Hamadani in 1310, to date his arrival in Egypt at 30 August 1078.

The news of this Ismā'īlī's activities reached Nizam al-Mulk, who dispatched his soldiers with the orders for Hasan's capture.

[citation needed] His search for a base from which to guide his mission ended when in 1088 he found the castle of Alamut in the Rudbar area (modern Qazvin, Iran).

[17] While legend holds that after capturing Alamut Hasan devoted himself to isolated study, this narrative is highly doubtful, given his extensive recruiting and organizational involvement in the growing Ismā'īlī insurrections in Persia and Syria.

[18] The leaders of Nizari Isma'ilis in Persia, were designated by Marco Polo using a Syrian equivalent term known in Europe at that time,[19] as Elder or Old Man of the Mountain.

It developed during the struggle for succession of Nizar to the Fatimid throne in Cairo that eventually laid the foundation of the Nizari Isma'ilism Shia Islam.

An important task of the latter is the proliferation of the doctrine, and of the undisclosed imam's spiritual guidance, in learning centers having instructors proficient in teaching techniques.

Devotion of the "true believers" having "absolute faith"[23] in the beliefs is another element originating from the times of Sabbah in Northern Iran,[24] who reportedly "was so devout that he even had one of his sons executed after he was accused of drunkenness.

[27] Hassan was highly revered by the Nizari community, whose members called him Sayyidna ("Our Master") and regularly visited his mausoleum in Rudbar before it was demolished by the Mongols.