He was the only surviving son of Jalaluddin Hasan, whom he succeeded at the age of 9 years old, in 1221. However, upon succession he was initially too young, so Ḥassan III's vizier controlled the state. His mother was a Sunni woman and a daughter of one of the princes of Gilan. Alauddin Muhammad or Muhammad III was born in 609/1213. He was succeeded by his father at the age of 9 years. The administration of the state affairs had been governed by his gifted mother for about six years, which was the first instance when a woman administered at Alamut. The period of six years was very peaceful in Alamut, during which time the Imam's mother seems to have deposed many incapable governors in Rudhbar and Kohistan. It seems that some governors and officers had misused their powers in that period. In 624/1227, Alauddin Muhammad took the power upon the death of his mother at the age of 15 or 16 years and dealt iron-handed with the persons misusing the powers. Most of them turned against him and went to live in Qazvin. In order to cover the story of their defalcations, they started to spread rumors against the Imam in bitter sarcasm. Some of them went on to propagate that the brain of Alauddin Muhammad had been affected a few months before 624/1227 when a physician operated him, causing waste of excess blood. The oppositions were however surmounted very soon. Under Muhammad III's reign, the Sunni conformity initiated by his father was gradually and quietly reversed and his community increasingly regarded itself openly as IsmailiShi'ite. His rule was described as "cruel, imperious, sadistic, alcoholic, and unpredictable." The Mongol invasions of Nizari strongholds in Quhistan in 1253 and the imminent arrival of Hülegü's army in 1255 incited internal conflicts upon Nizaris. The relationship of Muhammad, who had reportedly been afflicted by melancholia and mental deterioration, was deteriorated with his advisors and Nizari leaders, as well as his son Rukn al-Din Khurshah, who was supposed to be the future Imam. According to Persian historians, the Nizari elites prepared a plan against Muhammad to replace him with Khurshah, who would then enter into immediate negotiations with the Mongols; however, Khurshah fell ill before implementing this plan. Soon afterward, on 1 December 1255, Muhammad was murdered in suspicious circumstances in Shirkuh near Alamut and was succeeded by Khurshah. The murderer was later found to be Muhammad's companion Hasan Mazandarani, as revealed by his wife. Mazandarani and three of his children were later executed by Khurshah, as retribution.
