1. Birth and Titles
Imam ʿAlī b. Mūsā al-Riḍā (a.s.), the eighth Shi'ite Imam was born on 11th Dhīqaʿda 148 A.H. in the holy city of Medina. His name is ʿAlī, his title is Abu al-Ḥasan, and his most famous honorary name is ‘Riḍā’, meaning ‘Satisfaction’.  According to his son, Imam Jawād (a.s.), the ninth Imam, “The Glorious and Mighty Lord named him Riḍā because Allah was pleased with him in the heavens and the Prophet of Allah (a.s.) and the Imams of guidance (a.s.) were pleased with him on earth. Also, his friends and relatives and even his enemies were satisfied with him (because of his great moral qualities)”.One of his famous titles is ʿĀlim Ale Muḥammad 

2. Father and Mother
His mother, Najma (a.s.), after Imam Riḍā (a.s.) was born, his mother handed him to his father, Imam Kāẓim (a.s.), who whispered the Adhān statements in the right ear of the newborn and the Iqāma statements in the left. Then Imam Kāẓim (a.s.) said, “This son will be Allah’s argument-person on the earth and the Imam after me”.

His life in Medina
Before traveling to Marv, Imam Riḍā (a.s.) lived in Medina; city where the shrine of Prophet Muḥammad and his father’s grave exists. He was occupied with guiding people, indicating Islamic educations and Prophet’s (manner and behavior). People of Medina loved him and assumed him as their father. Although he had spent most of his life in Medina, he had many followers throughout the Islamic counties. He points out this fact on a discussion about succession, “In fact succession didn’t make a distinction for me. When I was in Medina, people in east and west obeyed me and nobody was superior to me. They told me their requirements and I granted their requests and they treated me as a magnate.”

His Imamate
Imam Riḍā’s (P.B.U.H.) Imamate was announced repeatedly by his father, grandfathers, and Prophet Muḥammad (P.B.U.H. & H.H.). Especially Imam Kāẓim (P.B.U.H.) mentioned him as the Imam after himself several times. For instance, one of his followers narrates, “One day Imam Kāẓim (P.B.U.H.) came to us, holding his son’s hand. We were 60 people. He said, ‘Do you know me?’ I said, ‘You are our leader.’ He said, ‘Say my name and title.’
I said, ‘You are Mūsā b. Jaʿfar b. Muḥammad.’ He said, ‘Who is this with me?’
I said, ‘ʿAlī b. Mūsā b. Jaʿfar’. He said, ‘So profess that he is my representative during my life and my successor after my death.’” He is further introduced as the eighth Imam in a saying of Prophet (P.B.U.H. & H.H.) narrated by Jābir.  Also, Imam Ṣādiq (P.B.U.H.) told Imam Kāẓim (P.B.U.H.) that the knowledge of Prophet’s (P.B.U.H. & H.H.) progeny is of your sons and he is your successor.
 
Political Situations
Imam Riḍā’s (P.B.U.H.) Imamate lasted twenty years, which can be divided into three periods:
1-The first ten years was contemporary to Hārūn’s caliphate.
2-The next five years was contemporary to Amīn’s caliphate.
3-The last five years was contemporary to Maʿmūn’s caliphate.
It was during the first period that great disasters, especially the martyrdom of Imam Kāẓim (P.B.U.H.), happened to the ʿAlavīd people (the children of Imam ʿAlī (P.B.U.H.)). Hārūn was instigated to kill Imam Riḍā (P.B.U.H.), but had not found the opportunity. After Hārūn, Amīn became the caliph. At that period, the government was weakened. Amīn was drowned in his corruption and paid no attention to Imam (P.B.U.H.) and his followers. This period was peaceful for Imam (P.B.U.H.) and his followers.
However, Maʿmūn killed his brother, Amīn, and became the caliph. He suppressed the objectors and gained the control of all the Islamic countries. He then chose Faẓl b. Sahl, who was a great politician, as his minister. But the ʿAlavīd people were a threat to his government. After suffering murder, plunder and torture for a century, they had found the opportunity to object the government and to overthrow it. They were successful in gaining people’s support, because they also had suffered great losses from the Abbasid caliphate. Therefore, Maʿmūn decided not to confront them and wanted to bring back peace and security to strengthen his government.