When Saddam Hussein fell, they quickly took control of a Baghdad suburb that is home to about two million Shiite Muslims. Now the young clerics of the al-Sadr group publish a weekly paper, operate courts and run a welfare system, and they repeatedly rally thousands of supporters for Baghdad street protests as a show of strength.
They are disciplined and hungry for power. But their ambitions are running up against the US-led occupation force as well as other Shiite factions, which have been angered by the al-Sadr clerics' claim to be the only clerics with the right to lead Friday prayers for Shiites everywhere in Iraq.
The group's leader, Sheik Muqtada al-Sadr, is not yet 30, and his followers are mostly in their 20s or 30s. They are striving tirelessly to replace more traditional factions as the voice of Iraq's Shiite majority, portraying themselves as the ones doing the most to redress decades of suppression by Sunni Muslims.
After swiftly taking control of the Baghdad suburb that is home to Iraq's single largest concentration of Shiites, al-Sadr clerics opened a smoothly run campaign to repair power plants and telephone exchanges and to provide security.
What resembled an informal relief agency back in April has given way to a government-like operation run by men confident enough to turn down an invitation to join a US-backed city council and to organize elections for managers of the district's neighborhoods. The group also is preparing to open their own television channel.
US officials and others argue that the influence of al-Sadr clerics is largely confined to "al-Sadr city," the poor and overcrowded Baghdad district once known as Saddam City. Some people feel Sheik al-Sadr's standing stems not from his own accomplishments but from being the son of Mohammed Sadiq al-Sadr, a leading cleric killed by Saddam's agents in 1999.
Al-Sadr claims tens of thousands of volunteers have come forward to join a religious army he wants to create to drive US forces out of Najaf, Iraq's holiest Shiite city, and to beat back what he calls the corrupt influences brought by the Americans.
Officials of Iraq's US-led administration believe al-Sadr and his followers are not welcome in Najaf, a view that was underlined when al-Sadr criticized the people of Najaf on Saturday for not showing proper backing for protests against US occupation of the holy city.
"Muqtada al-Sadr is not important in this city," Marine Lieutenant Colonel Christopher Conlin, the coalition commander in Najaf, told reporters this past week. "He is a young and immature man who is living off his father's name. He has little support here."
Al-Sadr has sharply criticized the Governing Council set up by the US this month to run Iraq. He brands the 25-member body of representatives from various religious and ethnic factions a tool of America that must be opposed and calls for the establishment of a rival "popular council."
But he has little to say when asked about his vision of Iraq's political future.
"I am not a Western person who plans so far ahead. I take a first step and wait for what happens next," he said when asked how he plans to form a rival council.
Although recent street protests by al-Sadr followers have irked the US-led coalition, it has so far not taken any punitive measures, primarily because of the group's repeated assertions that it will employ only peaceful means to seek an end to the occupation.