Imam (A) was brought up under the care of his father for 35 years. His father left behind a written document declaring his succession.

Imam (A) is also known as Imam Zaamin (A). Zaamin comes from the Arabic word Zamaanat, which means security. Whenever we start a journey, we pray to Allah to keep us safe for the sake of our eighth Imam (A). We also give some money in charity, which is in the name of Imam Zaamin (A).

When his father was poisoned in prison in 183 A.H., Imam (A) took over the great responsibility of Imamat under very difficult circumstances. Haroon Rashid, the Abbaside Caliph, made life very difficult for the followers of Imam (A).

In Madina, Imam (A) carried out his duties in a peaceful manner in the face of a very difficult period for the Shia, and it was mostly due to his efforts that the teachings of the Holy Prophet (S) and the correct interpretation of the Holy Qur'an became widespread. He had command over several languages and used to answer the questions of his followers in their own language.

Haroon Rashid died in 193 A.H., having nominated his son Amin as his successor. However, Amin was killed after ruling for 4 years only, by his brother Ma'mun, who then took over the Abbaside Caliphate.

Ma'mun was an intelligent man, and he could see that the Shia were increasing in number despite torture and oppression. He was aware of the position and power that Imam (A) held over the people. Many of Ma'mun's own ministers were Shia, and he began to get worried about the influence of Imam (A).

He decided that the only way he could hold on to power and quieten down the Shia, who were threatening to revolt, was by changing his approach.

First, he declared himself Shia also. He ordered that the descendants of Imam Ali (A) should not be harmed. Next, he invited Imam (A) to come from Madina to Marv, which was his winter capital.

On his way to Marv, Imam (A) passed Nishapoor, where thousands of people had gathered to catch a glimpse of him. Some scholars begged him to stop and address them so that they could hear his voice. Imam (A) related to them that the angel Jibraeel (A) had told the Holy Prophet (S), who had told Imam Ali (A), and each Imam (A) had told the next Imam (A), that Allah had said, "Laa Ilaaha Illallah is My fortress, and whoever enters My fortress saves himself from My punishment." Then Imam (A) went forward a little and stopped. He then informed them that there were a few conditions to entering the fortress of Allah, one of which was complete submission to the Imam (A) of the time. This report is famous and has been recorded by many historians.

On his arrival in Marv, Imam (A) was met with respect by the hypocrite Ma'mun. He admitted that Imam (A) had the right to the Caliphate, and offered it to him. Imam (A) refused and so Ma'mun insisted that he accept to become the heir to the throne.

Despite his reluctance, Imam (A) was forced to accept the position, and Ma'mun made the people pay the oath of allegiance to him. He also ordered that the royal robes would be green in the future, which was the colour of the household of the Holy Prophet (S). Ma'mun then ordered that the Dirham coin should have the name of Imam (A), and issued a royal decree saying that Imam (A) would succeed him and his title would be ar-Riza min Aale Muhammad.

Ma'mun had not given this position to Imam (A) due to any love for him, but he had done it to quieten the threat of the Shia. He had no intention of allowing Imam (A) to become his successor. When Imam (A) took up his place in the court of Ma'mun, he took the opportunity to spread the teachings of Islam further. He organised Majalis to remember the martyrs and sacrifice of Karbala, and explained to the people the moral lessons to be learnt from that tragedy.

Ma'mun's court was visited by people from all over the world. Imam (A) answered all the questions they asked to Ma'mun. They were always satisfied with his answers, used to say that they had never met a man who argued and explained in the style of Imam (A).

Ma'mun soon felt threatened by the growing popularity of Imam (A) and decided to ensure his own survival by killing him. He did this by inviting Imam (A) to a meal where he fed him poisoned grapes. Imam (A) became very ill as a result and died on 29th Safar 203 A.H. He is buried in Toos (Mashad) in Iran.