Hasan-i Sabbah

Hasan-i Sabbah (c. 1050 – 12 June 1124; AH 518), also known as Hasan I of Alamut, was a military leader, scholar, and founder of the Nizari Ismaili movement, popularly known in the West as the Order of Assassins, as well as the Nizari Ismaili state, which he ruled from 1090 until his death in 1124. Very little is known of his early life.

His followers seized the formidable mountain fortress of Alamūt in 1090 or 1091 (AH 483) and established it as the principal power centre of the Nizari movement. Although the movement later became particularly associated with assassination, al-Sabbah did not introduce assassination as a religious duty, since the practice had already been employed by other sects, and it is not clear that he himself even advocated it. The movement that developed under and after him nevertheless acquired considerable strength and terrorized parts of the Muslim world until Alamūt was captured and destroyed by the Mughals in the 13th century.

Alongside his political and military leadership, al-Sabbah was a scholar of mathematics, particularly geometry, as well as astronomy and philosophy, especially epistemology. It is also narrated that he and the Persian polymath Omar Khayyam were close friends from their student years. Hasan and later leaders of the Order of Assassins became known in Western tradition as the "Old Man of the Mountain", a designation associated by Marco Polo with the sect's possession of the commanding fortress of Alamut.

Notable works: Fusul-i Arba'ah, Haft-Bab-i Baba Sayyidna, The Tale of the Three Schoolfellows, Sarguzasht-i Sayyidna, Dastur al-Munajjimin Education: al-Azhar Mosque, House of Knowledge

Source: Wikipedia — https://en.wikipedia.org/wiki/Hasan-i_Sabbah