One of the most eminent Ismaili dais during this period was Abu Hatim ar-Razi, the hujjat of Ray. He was born near Ray around 260/874. He conducted the mission with great efficiency and promptness. He was a remarkably learned dai, and studied Ismaili doctrines, but also Arabic poetry, the religious science of Islam, comparative religion and indeed the natural and mathematical sciences of the day. He succeeded to bring the ruler of Ray, Ahmad bin Ali (307-311/92O-924) to the Ismaili fold, who was formerly aggressive to the Ismailis. Abu Hatim also deputed his subordinate dais in Tabaristan, Ispahan, Azerbaijan and Jurjan; resulting a large conversion, including Mardav ad-Daylami, the governor of Tabaristan; Yousuf bin Abi'l Saj, the governor of Azerbaijan, and Asfar bin Shroya. Abu Hatim was a great philosopher, orator and writer. W.Ivanow writes in "A Creed of the Fatimids" (Bombay, 1936, p. 5) that, "Abu Hatim ar-Razi surely was one of the most erudite authors that Ismailism, and generally, Islam has ever produced." Seyyed Hossein Nasr writes in the introduction of "A'lam al-Nubuwwah" (ed. by Salah al-Sawy, Tehran, 1977, p. 1) that, "He is one of the most outstanding theologians and philosophers of Islam and a major figure in that galaxy of exceptional thinkers, such as Hamid al-Din Kirmani, Nasir-i Khusraw and Qadi Numan, who produced the Ismaili philosophy of the Fatimid period."
The most acclaimed of his works is "Kitab az-Zina" designed as an encyclopaedia of Islamic terminologies with a large store of useful informations. Idris Imaduddin (d. 872/1468) writes in the 5th volume of "Uyun'l-Akhbar" that it was greatly admired by Imam al-Qaim when it was presented to him, and he gave it to his son, al-Mansur in a gift, commanding to keep it secret.
Abu Hatim left Ray in 311/924 and sided with Asfar bin Shroya (d. 319/931). He acquired many converts in Daylam and Gilan, including Asfar bin Shroya's deputy, Mardawij bin Ziyar (d. 323/935). According to Hamiduddin Kirmani in "al-Aqwal al-Dhahabiyya" (Tehran, 1977, pp. 2-3), "The famous disputation between Abu Hatim and the physician-philosopher, Abu Bakr Muhammad bin Zakaria ar-Razi (251-313/865- 925) took place in Mardawij's presence." The discussion concerning prophethood is given in his "A'lam al-Nubuwwah." He answered the questions of Zakaria ar-Razi that how he necessiated that only one nation would be favoured and given superiority over others. He also argued that his conception regarding the eternity of five principles, namely God, Soul, Matter, Space and Time was absurd. He also discussed logically the questions relating to blind faith, analogy, miracles etc.
Mardawij at first supported Abu Hatim, but started enmity against the Ismailis. Thus Abu Hatim returned to Ray, thence he proceeded to Azerbaijan and took refuge with a local ruler called, Muflih. He died in 322/934 in Daylam, and after him, the Ismailis of Khorasan and Transoxania became disordered, and finally their leadership came to the hands of Abdul Malik al-Kawkabi, who resided in Girdkuh, the future stronghold of the Nizari Ismailis.