Al-Sadr is the son of assassinated Shi'ite cleric Muhammad Sadiq al-Sadr.

The 31-year-old is said to be responsible for the killing of Washington-supported cleric Abd al-Majid al-Khoi in Al-Najaf on 10 April 2003.

Al-Sadr, who has little theological training, was appointed "deputy and representative in all fatwa affairs" by Qom-based Iraqi cleric Kazim al-Ha'iri in late April 2003.

His followers are known as the Sadriyun.

Al-Sadr has emerged as one of the most popular Shi'ite leaders in Iraq, and appeals to the poor and disenfranchised, who are drawn to the cleric's charisma and anti-U.S. stance.