Ruknuddin Hasan, surnamed Khurshah was born in 627/1230. He is also known as Kahirshah. When he was still a child, his father had declared him as his successor. Juvaini tried to adulterate the Nizarid line of Imamate, but at one place he curiously writes (p. 663), "And today, the leader (Ruknuddin Khurshah) of the heretics (the misnomer used for the Ismailis) of Alamut traces his descent from this son (of Nizar).
His father, Imam Alauddin Muhammad had taken due care of rudiments of his formal education at home under personal care. When he grew young, his father designated him his deputy to investigate few cases of disorders in some castles, with an instruction to obey his orders as his own. In 653/1255, before his father's death, he is reported to have visited Syria with a letter of his father. Strict protection had been given to Ruknuddin, and wherever he went, a small unit of armed men accompanied him as security guards. It is related that he stayed more than a year in the castles of Rudhbar and Kohistan for making fresh administrative fabric, and thus the enemies of the Ismailis smacked of exaggerations that his relation had been deteriorated with his father.
Three days later, having assumed the Imamate, Ruknuddin sent an army which his father had ordered against Shal-Rud in the district of Khalkhal. The Ismaili forces occupied the castle after a small fighting.