Final answer:
Imam Ja'far al-Sadiq is the author of Risala Dar Haqiqat-I-Din. As a significant figure in Shia Islam, he contributed much to religious and scientific scholarship. The legitimacy of Shia leaders is traced through descent from Ali, highlighting the importance of lineage.
Step-by-step explanation:
The author of Risala Dar Haqiqat-I-Din (True Meaning of Religion) is Imam Ja'far al-Sadiq. Imam Ja'far al-Sadiq is an important figure in Shia Islam and is considered the sixth imam by the Twelver Shia and the Ismailis. He is well-regarded for his scholarly contributions and is attributed with teaching many students in various fields of knowledge, including theology and science.
The legitimate caliphs in Shia Islam had to be descended from Ali, the first Imam, who was a cousin and son-in-law of Prophet Muhammad. Shia Muslims believe that the leader of their community should ideally be a descendant of Muhammad, which is one of the tenets one would learn in a Shia religious school. Additionally, Shah Ismail claimed that he was descended from Adam, Muhammad, and Ali, which highlights the importance of lineage in Shia Islam. The Shia also believe in the Twelve Imams, with Ali being the first and the twelfth being Muhammad al-Mahdi, who is believed to return alongside Jesus to herald the Day of Judgment.
The earliest supporters of Ali, who became the Shia, are defined by the elevation of the family of Muhammad through his son-in-law Ali. This family, known as the Ahl al-Bayt, is considered by Shia Islam to hold a special status. Additionally, the only Shia caliphate was established by the Fatimids, which indicates the importance of dynastic rule in the history of Shia political leadership.