Hasan bin Sabbah was an intelligent and proficient in geometry and astronomy. He learnt the Ismaili doctrines from a Fatimid dai, Amir Dharrab, who expounded him the doctrine of the Ismailis. Soon he was reading Ismaili literature, which so stirred him that when he became dangerously ill, he began to fear that he might die without knowing the truth. When he recovered, he approached an Ismaili for further clarification of the doctrines. Convinced that Ismailism represented ultimate reality, he embraced Ismailism at the age of 35 years in 464/1071 and afterwards, he came into contact with a Fatimid dai Abdul Malik bin Attash in Ispahan.
Hasan bin Sabbah writes in "Sar Guzasht-i Sayyidna" that, "In the year 464/1071 Abdul Malik bin Attash, who at that time was the dai in Iraq, came to Ray. I met with his approval, and he made me a deputy dai and indicated that I should go to His Majesty in Egypt, who at that time was al-Mustansir. In the year 469/1077, I went to Ispahan on my way to Egypt. I finally arrived in Egypt in the year 471/1078." In sum, Hasan moved from Ray to Ispahan in 467/1074. Later on, when al-Muayyad was the chief dai at Cairo in 469/1077, he set out from Ispahan for Egypt. He travelled at first to northern Azerbaijan, thence to Mayyafariqin, where he held religious deliberations with the Sunni theologians and denied the right of Sunni muftis to interpret religion, that being the prerogative of the Imam. As a result, he was expelled by the town's Sunni qadi. He proceeded to Mosul, Rahba and Damascus. He sailed through Beirut, Sidon, Tyre, Acre, Caesarea and finally reached Cairo in 471/1078. Imam al-Mustansir gave him audience and honoured him. Hasan asked him as to who would be the Imam after him. Al-Mustansir replied that it would be his son Nizar. He is reported to have stayed 18 months in Cairo, enjoying the patronage and favour of his master. He also learnt latest tactics of the dawa in Dar al-Hikmah, which was in those days the biggest learning centre of Islam. Hasan, thus profited much by his journey to Egypt. It is possible that he had a meeting also with al- Nizar in Cairo. Laurence Lockhart writes in "Hasan-i Sabbah and the Assassins" (BSOAS, vol. v, 1928, p. 677) that, "Hasan was well received at Cairo, and was treated with marked favour by the Fatimid Caliph al-Mustansir. It is said by some writers that Hasan received so many benefits at the hands of the Caliph that the courtiers became jealous, and eventually forced him to leave the country." Badr al-Jamali, the Fatimid vizir however was the foremost to breed suspicion, when he knew that Hasan was the supporter of al-Nizar bin al- Mustansir, therefore he got Hasan imprisoned in the fortress of Dumyat. The strong walls of the fortress collapsed one day, enabling him to escape. He boarded a vessel at Alexandria with a group of Franks for western waters, but the stormy winds tossed his vessel on the shores of Syria and he alighted at the port of Acre. Then onwards, he toured many cities; studied the economic, social and religious conditions of the people. He reached Ispahan in 473/1081 and began to propagate Ismaili faith in Yazd and Kirman for a while. He spent three months in Khuzistan before proceeding to Damghan, where he stayed about three years.
There was plenty of mission activity, pervasive throughout its length and breath in Iran under the control of Abdul Malik bin Attash. In about 480/1088, Hasan bin Sabbah seems to have chosen the remote castle of Alamut in Daylam as the base of his mission. He sent from Damghan, and later, from Shahriyarkuh, a number of trained dais, including Ismail Qazwini, Muhammad Jamal Radi and Kiya Abul Kassim Larijani to different districts around Alamut valley to convert the local inhabitants. Hasan, at length was appointed a dai of Daylam. In the meantime, the Seljukid vizir, Nizam al-Mulk (408-485/1018-1092), a well known implacable foe had ordered Abu Muslim, the governor of Ray to arrest him. Hasan however managed to proceed to Daylam in hiding. He then reached Qazwin (also called Qasbin or Qashwin) , and inspected the fort of Alamut in Rudhbar. He remained in worship within the fortress, and also converted the local people. He took possession of the fortress of Alamut in 483/1090 and established an independent Nizari Ismaili state.
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