Ḥasan Ṣabbᾱḥ was a terrifying rival for his contemporaries and authoritative and charismatic ruler for his followers. For today’s historians, he is one of the most exciting figures of medieval Islamic history. His name and the name was given to his followers, assassins remind modern readers some sense of terrorism and amazing adventures. However, Ḥasan Ṣabbᾱḥ was more than biased judgments. Even, for Bernard Lewis he was a “revolutionary genius”.  Ḥasan Ṣabbᾱḥ was one of the most important Ismāʿīlī dāʿīs (missionary) and he is the founder of the Nizārī Ismāʿīlī state in Alamūt which is in Alburz mountains, in the Rūdbār (or Daylamān) region. He was born in Qom, in the mid-1050s, or around 1048, and he died in Alamut in 1124. We know little about his early life and what we know about this period, also what all the secondary sources tell us, is mainly came from Sargudhasht-i Sayyidna (The biography of Sayyidnā), the first part of which may have been autobiographical. Neither the autobiography of Ḥasan Ṣabbᾱḥ not Sargudhasht-i Sayyidna is available today. What lasted to us is the fragmented accounts which were preserved by later Persian historians: Juwaynī (d. 681/1283), Rashīd al-Dīn (d. 718/1318), and Abū l-Qāsim Kāshānī (d. c.738/1337). In the surviving accounts that are quoted by Bernard Lewis, Ḥasan Ṣabbᾱḥ tells about his childhood and the first acquaintance with Ismāʿīlī doctrines.
“From the days of my boyhood, from the age of seven, I felt a love for the various branches of learning, and wished to become a religious scholar; until the age of seventeen I was seeker and searcher for knowledge.
In Rayy I met a man, one of the comrades (Rafiq, a term often used by the Ismailis of themselves] called Amīra Ḍarrāb, who from time to time expounded the doctrine of the Caliphs of Egypt (…)
There had never been any doubt or uncertainty in my faith in Islam; in my belief that there is a living, enduring, all-powerful, all-hearing, all-seeing God, a Prophet and an Imam, permitted things and forbidden things, heaven and hell, commandment and forbidding. I supposed that religion and doctrine consisted of that which people in general, and the Shia in particular, possessed, and it never entered my mind that truth should be sought outside Islam. I thought that the doctrines of the Ismailis were philosophy [a term of abuse among the pious], and the rule of Egypt a philosopher.
Amīra Ḍarrāb was a man of good character. When he first conversed with me, he said: “The İsmailis say such and such.” I said, “O friend, do not speak their words, for they are outcasts, and what they say is against religion.” There were controversies and debates between us, and he disproved and destroyed my belief. I did not admit this to him, but in my heard these words had great effect (…) ” (Lewis 2002, 31-32)
Sargudhasht-i Sayyidna also tells a legend in which Ḥasan Ṣabbᾱḥ, the vizier of Saljūqs, Niẓām al-Mulk (d. 485/1092), and the famous poet ʿUmar Khayyām (d. c. 517/1123) were schoolfellows at Nīshāpūr, and which is repeated by other Persian historians. However, modern historians came to an agreement that this is a mere myth  even though some says that this case is real. 
Ḥasan Ṣabbᾱḥ’s family was a Twelver Shi’ite family. His father, ʿAlī b. Muḥammad b. Jaʿfar b. al-Ḥusayn b. Muḥammad b. al-Ṣabbāḥ al-Ḥimyarī was a Kufan who claimed to have their origins from Himyarite Yemenites. ʿAlī b. Muḥammad had migrated Kufa to Qom. They eventually migrated to Rayy in which Ḥasan Ṣabbᾱḥ took his first religious education with the Twelver Shi’ite tradition. Rayy, since the 9th century was a center of Ismāʿīlī doctrines and so, Ḥasan Ṣabbᾱḥ was first introduced these doctrines by Amīra Ḍarrāb who was a local Ismāʿīlī dāʿī. Initially, he was suspicious about Ismāʿīlī doctrines, but he also learned more from other local dāʿīs of Rayy. Ultimately when he was seventeen, Ḥasan Ṣabbᾱḥ took the ‘ahd (oath) to Ismāʿīlism and the Ismāʿīlī imam of that time who was also the Fatimid Caliph, al-Mustanṣir (1036-94).
The young Ḥasan Ṣabbᾱḥ was appointed to a position in the daʿwa (mission) by the chief Ismāʿīlī dāʿī of Seljuq territories, ʿAbd al-Malik b. ʿAṭṭāsh who was “responsible” for the early career of Ḥasan Ṣabbᾱḥ in Ismāʿīlism. In 1074-75 Ḥasan Ṣabbᾱḥ went to Isfahan, the secret headquarters of the Ismāʿīlī daʿwa in Persia, with b. ʿAṭṭāsh. He stayed there until 1076-77. After the order of b. ʿAṭṭāsh, he left Isfahan to Cairo, for further Ismāʿīlī education. He reached Egypt in 1078 and spent three years of his life firstly in Cairo then in Alexandria. (cite)  However, a little is known about his experiences in Egypt. What we know is that his beliefs clashed with the ones of vizier Badr al-Jamālī and eventually Ḥasan Ṣabbᾱḥ left Egypt. He returned to Isfahan in 1081.
After travels over several years in the mission, Ḥasan observed the military strength of the Seljuqs and established his own revolutionary strategy against them. By 1087, he had been active mainly in the region of Daylamān that was a stronghold of Shi’ism in Persia and that was also far from the direct authority of Seljuqs. Then, he became the dāʿī of Daylamān and stimulated the daʿwa in northern Persia. Eventually. He seized the fortress of Alamut in 1090. This marked the foundation of Isma’ili state in Persia that rioted against the Seljuqs.
Ḥasan Ṣabbᾱḥ was fiercely against the Seljuqs who were Sunnis and that were attacking o Shi’ism and the Shi’ite Fatimid caliphate. According to some, Ḥasan Ṣabbᾱḥ ‘s revolt may have been not only because of his religious identity but also because of the Persian hatred against Seljuq Turks. He was also so aware of his ethnic identity that he replaced Arabic with Persian as the religious language of the Persian Ismāʿīlīs.
Ḥasan Ṣabbᾱḥ strengthened the fortress and made the Alamut valley self-sufficient in terms of agricultural production, after his developments in cultivation and irrigation systems. He also established a significant library in Alamut. This library was destroyed by the Mongols in 1256 but it had a significant reputation in time. In this library, some important scholars also grew up. One of those important scholars was Nasīr al-Dīn Tūsī who studied philosophy, astrology, mathematics, and theology of Shi’ism. The other one was a great historian Rashīd al-Dīn, according to Fuat Köprülü. 
Ḥasan Ṣabbᾱḥ did not stop after he seized the fortress of Alamut. Along with it he built new fortresses in Rūdbār region and converted more people. The continuous Seljuq- Ismāʿīlī battles were marked when Alamut raided by a Seljuq amīr. In 1091, Hasan sent Ḥusayn Qāʾinī to his native land in Khorasan to mobilize a support. This action stimulated an uprising against Seljuqs. Eventually, Ismāʿīlīs seized control of several towns in Qohestan and along with Rūdbār, Qohestan became an area in which Persian Isma’ili activity took place. Two years later he took the Alamut, Ḥasan Ṣabbᾱḥ managed to establish an independent state in the Seljuq Empire. 
In these battles, Ismāʿīlīs took the advantage when they could assassinate the powerful Seljuq vizier Niẓām al-Mulk that followed the death of the Sultan Malek-šāh. In these circumstances of disorder, Ḥasan Ṣabbᾱḥ expands his rule and power in Rūdbār. He also captured the strategically important fortress of Lammasar (Lanbasar) along with several castles, including Gerdkuh and Arrajan.
Ḥasan Ṣabbᾱḥ had unique methods of the challenge against the Seljuqs. He was aware of the decentralized nature of Seljuq Empire so that his plan was to kill off each Turk amīr via his followers. His most famous technique was assassination so that this usage of assassination soon became specified with the Ismāʿīlī. The instructions of Ḥasan Ṣabbᾱḥ was carried out by his followers that were called fedāʾis (sacrificing devotees).
Another struggle of Ḥasan Ṣabbᾱḥ originated in the Egypt over the successor of the Fatimid Caliph, al-Mustanṣir. The dispute over succession caused a schism in Ismāʿīlīs and divided them into two rival groups: Nizārī and Mustaʿlī. Ḥasan Ṣabbᾱḥ was supporting Nizār who was al-Mustanṣir’s eldest son and designated successor. However, the Fatimids and Isma’ilis in Cairo were supporting Nezar’s younger brother, called al-Mustaʿlī and appointed him to the Caliphate. Hence, Ḥasan Ṣabbᾱḥ split his Ismāʿīlī daʿwa from Cairo, known as Nizārī, and he was confirmed by Ismāʿīlīs of Persia and Iraq who were known as the Nizāriya.
Ḥasan Ṣabbᾱḥ, beginning with the 12th century sent his dāʿīs to Syria. After some fifty years, representatives of Nizārī state in Persia could capture permanent settlement in Syria and they established the sole Ismāʿīlī existence there. Also, after the murder of Nizār, Ḥasan Ṣabbᾱḥ ‘s himself ruled Nizārī Isma’ili daʿwa as well as the state. His rank was hojja (chief representative of the hidden Imam).
Ḥasan Ṣabbᾱḥ was also a prominent theologian who wrote a dissertation called Fuṣūl-i arbaʿa (The Four Chapters) which is established on the basis of the Shi’ite doctrine of taʿlīm (authoritative instruction). Fuṣūl-i arbaʿa was written is Persian but it did not survive. Like the life of Ḥasan Ṣabbᾱḥ what we know about this dissertation comes from later Persian historians. Among Hasan’s main thesis was the inability to know the God in the absence of the Isma’ili Imam. Ḥasan Ṣabbᾱḥ was so devoted to his daʿwa that from the time Ḥasan Ṣabbᾱḥ captured the castle of Alamut until his death, he never left the castle and only twice left his house. According to Rashīd al-Dīn, “The rest of the time until his death he passed inside the house where he lived; he was occupied with reading books, committing the word of the da’wa to writing, and administering the affairs of his realm, and he lived an ascetic, abstemious, and pious life.”
Ḥasan Ṣabbᾱḥ died on 12 June 1124, after he appointed Kiyā Buzurg-Umīd (1124–38) as his successor. Until it was destroyed by the Mongols in 1256, his mausoleum had been visited regularly by Nizārī Ismāʿīlīs.
 (Lewis 2002, 30)
 (Maalouf 2015)
 (Daftary, The Isma’ilis: Their History and Doctrines 2009, 311)
 (Daftary, The Isma’ilis: Their History and Doctrines 2009, 303-306)
 (Lewis 2002, 33) (Daftary, The Isma’ilis: Their History and Doctrines 2009, 312) (Lockhart 1930, 676) (Rizvi 1980)
 (Rizvi 1980, 234)
 (Daftary, The Isma’ilis: Their History and Doctrines 2009, 311)
 (Lockhart 1930, 677)
 Farhad Daftary, “ḤASAN ṢABBĀḤ,” Encyclopaedia Iranica, XII/1, pp. 34-37, available online at http://www.iranicaonline.org/articles/hasan-sabbah (accessed on 30 December 2012).
 (Köprülü 2014, 104-105)
 Daftary, Farhad, “Ḥasan-i Ṣabbāḥ”, in: Encyclopedia of Islam, THREE, Edited by: Kate Fleet, Gudrun Krämer, Denis Matringe, John Nawas, Everett Rowson. Consulted online on 25 November 2017 <http://dx.doi.org/10.1163/1573-3912_ei3_COM_30361>
First published online: 2016
 (Daftary, The Isma’ilis: Their History and Doctrines 2009, 340)
 (Lewis 2002, 36)
Daftary, Farhad, “Ḥasan-i Ṣabbāḥ”, in: Encyclopaedia of Islam, THREE, Edited by: Kate Fleet, Gudrun Krämer, Denis Matringe, John Nawas, Everett Rowson. Consulted online on 25 November 2017 <http://dx.doi.org/10.1163/1573- 3912_ei3_COM_30361> First published online: 2016
Farhad Daftary, “ḤASAN ṢABBĀḤ,” Encyclopaedia Iranica, XII/1, pp. 34-37, available online at http://www.iranicaonline.org/articles/hasan-sabbah (accessed on 30 December 2012).
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Lockhart, Laurence. “Ḥasan-i-Ṣabbāḥ and the Assassins.” Bulletin of the School of Oriental and African Studies, February 1930, 5 ed.: 675-696.
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