Muqtada al Sadr, one of the most popular Shiite clerics and an unrelenting rival of the United States in Iraq, has returned to his home in the southern Iraqi city of Najaf after three years of self-imposed exile in Iran. The cleric's surprise homecoming is a victory lap after he played a role as kingmaker in ending months of political paralysis and securing a second term for the Iraqi prime minister, Nouri al al Maliki.
Under pressure from Iran, Mr al Sadr finally agreed to Mr al Maliki's bid to remain in office. With Mr al Sadr's backing, the prime minister was able to reach a deal with other political factions, especially the Kurds. That allowed Mr al Maliki to secure a majority in the 325-seat Parliament, which was necessary to approve a new government.
Now, Mr al Sadr has returned home to play a central part in Iraqi politics and to oversee his movement's transition from a militia force to a powerful political group with 40 seats in Parliament. But his ascendance threatens to stoke sectarian tensions in Iraq: his followers were responsible for some of the worst atrocities against Sunnis during the country's recent civil war. Mr al Sadr's militia, the Mahdi Army, unleashed death squads that assassinated Sunnis and drove them out of Shiite neighbourhoods.
It is not clear if Mr al Sadr has decided to return permanently to Iraq, or whether he intends to go back to Iran to resume his religious studies. In either case, his arrival on the Iraqi scene is carefully timed and intended to ensure that Mr al Maliki follows through on the promises he made to win the support of Mr al Sadr's parliamentary bloc.
Mr al Maliki is facing pressure from his political partners on several national security issues that could further polarise Iraq. The most important is whether Mr al Maliki would request that some US troops remain in Iraq beyond the end of the year, when they are obligated to depart under a 2008 security agreement. Days after he was nominated for a second term, Mr al Maliki said it would not be necessary to keep a small US force to continue training Iraqi troops and help maintain security.
Mr al Sadr's supporters have vowed to withdraw from Mr al Maliki's government if there is any attempt to keep a US military presence in Iraq beyond the end of this year. With such a fragile coalition keeping him in power, Mr al Maliki cannot afford to lose the support of Mr al Sadr's 40 seats in Parliament.
Mr al Sadr represents the triumph of a defiant brand of Shiism in Iraq. Because Grand Ayatollah Ali al Sistani and other senior theologians shun direct political involvement, they create a power vacuum among Iraqi Shiites - one that Mr al Sadr is eager to fill. He wants to be both a respected cleric and a political broker.
In the struggle for power within the Shiite community, Mr al Sadr had two claims to leadership: he is the son of a revered cleric killed by Saddam Hussein's regime, and he did not leave Iraq to live in comfortable exile during Saddam's rule. Mr al Sadr's father, Grand Ayatollah Muhammad Sadiq al Sadr, was one of the pre-eminent scholars of the Shiite world. Unlike Ayatollah Sistani, the elder Sadr argued that clerics should be involved in social and political matters.
Amid the euphoria that followed the ouster of Saddam's regime in 2003, clergymen debated their role in politics. Mr al Sadr and his supporters argued that they must fill the void left by the Baathist system. They denounced the US occupation and American plans to install an interim government made up mainly of exiled Iraqi politicians such as Ahmad Chalabi and Iyad Allawi.
Mr al Sadr's followers seized control of hospitals, schools and mosques in parts of Baghdad, Najaf and Karbala. He drew tens of thousands to his rallies and Friday sermons. He created the Mahdi Army, which had several thousand fighters - most of them young, impoverished Shiites from Baghdad's slums and southern Iraq.
Since he emerged as the fiercest Shiite critic of the US occupation, Mr al Sadr has been remarkably adept at using religious symbols to position himself as heir to a long line of Shiite martyrs. By doing so, he has tapped into a central tenet of Shiism: dying in defence of one's beliefs, as the sect's founders did in the seventh century. During months of traveling around Iraq in 2003 and 2004, I saw the same poster hanging in homes and on walls of Shiite neighborhoods: Muqtada cradling his assassinated father, blood dripping from his forehead and chest. The elder Sadr is holding up a copy of the Quran. The faceless shadow of Shiism's founding figure, Imam Ali, looms over father and son.
In reality, Muqtada was not with his father when agents of the Baathist regime gunned him down in 1999. The cleric's two eldest sons were with him, and they too were killed. But the painting is one example of how Muqtada has used his father's martyrdom to build support among Iraqi Shiites. And it helps explain why young Iraqis were willing to die for him, even as senior clerics urged them to avoid confronting US forces.
Mr al Sadr started out as a militia leader, with the populist appeal and credibility that comes from being heir to a family of martyrs. He then turned himself into one of Iraq's most effective politicians. The elder clerics watched from the sidelines, confident that their rarefied religious authority would be more enduring than the young upstart's fleeting political power.
But now Mr al Sadr is on his way to becoming an even more formidable power broker in Iraq.
Mohamad Bazzi is a journalism professor at New York University and an adjunct senior fellow at the Council on Foreign Relations