But even with his unmatched influence, Sadr proved unable to end a prolonged stalemate over forming a government, and so on Sunday lawmakers from his Sadrist bloc in parliament resigned after he asked them to step down.

Sadr, a populist who has positioned himself as a staunch opponent of both Iran and the United States, said he made the move as "a sacrifice from me for the country and the people to rid them of the unknown destiny".

Despite the withdrawal, Sadr still wields huge clout, with hundreds of thousands of followers who can stage protests, and his move sharply raises the stakes in the struggle for power within Iraq's Shi'ite majority.

Sadr was virtually unknown beyond Iraq before the 2003 U.S.-led invasion. But he soon became a symbol of resistance to occupation, deriving much of his authority from his family.

Sadr is the son of revered Grand Ayatollah Mohammed Sadeq al-Sadr, who was assassinated in 1999 after openly criticising then-dictator Saddam Hussein. His father’s cousin, Mohammed Baqir, was also killed by Saddam, in 1980.

"His family legacy - without it I don’t think he could be where he is today," said Randa Slim, Senior Fellow at the Middle East Institute.

Despite the risks, Sadr never fled Iraq, unlike other prominent figures in post-Saddam governments who returned from exile in Iran and the West following the invasion.

SADDAM TAUNTED WITH CLERIC'S NAME

When Saddam himself was executed in 2006, convicted for the killings of 148 people in a mainly Shi’ite Muslim town a quarter century earlier, witnesses taunted him by chanting Moqtada’s name as he was led to the gallows, leaked footage showed.

Sadr was the first to form a Shi’ite militia that fought U.S. troops. He led two anti-U.S. revolts, prompting the Pentagon to call his Mehdi Army militia the biggest threat to Iraq’s security.

In 2004, the U.S. occupation authority issued an arrest warrant for Sadr and said it would kill or capture him in connection with the 2003 murder of moderate Shi’ite leader Abdul Majid al-Khoei, who the Americans had brought into the holy Shi’ite city of Najaf during the invasion.

Sadr denied any role in Khoei's killing and was never charged.

Sadr survived upheaval in the 19 years since his Mehdi Army took on the Americans with assault rifles and rocket-propelled grenades in alleys and streets of Baghdad and southern cities.

His followers also fought the Iraqi army, Islamic State militants and rival Shi'ite militias.

In Iraq's sectarian 2006-2008 civil war, the Mehdi Army was accused of forming death squads that kidnapped and killed Sunni Muslims. Sadr has disavowed violence against fellow Iraqis.

In 2008 Prime Minister Nuri al-Maliki, a Shi'ite and long-time rival of Sadr, ordered a major offensive that crushed the Mehdi Army in the southern city of Basra.

Later that year, Sadr ordered a halt to armed operations and declared the Mehdi Army would be transformed into a cultural and social organisation and renamed the Peace Brigades.

SADR REINVENTS HIMSELF

He later decided to compete in Iraq's byzantine politics and gained even more popularity along the way by promising to stamp out rampant state corruption.

With his trademark turban, the self-proclaimed champion of the dispossessed could mobilise hundreds of thousands of followers on the streets at will.

In 2016, Sadr’s supporters stormed parliament inside Baghdad’s fortified Green Zone after he denounced the failure to reform a political quota system blamed for rampant graft because political leaders used it to appoint supporters in key jobs.

Sadr issued an ultimatum.

“If corrupt (officials) and quotas remain, the entire government will be brought down and no one will be exempt.”

He ordered his faithful to end their sit-in at the gates of the Green Zone after Prime Minister Haider al-Abadi presented a new cabinet lineup meant to fight corruption.

Sadr rebranded himself before parliamentary elections in 2018, forming an alliance with Communists and secularists.

After being sidelined for years by Shi'ite rivals backed by Iran, he emerged victorious in a remarkable comeback, gaining control of ministries and civil service positions.

Sadr had tapped into public resentment with his former ally Iran and the political elite which Iraqis say supports it.

He was the only Shi'ite leader to challenge both Tehran and Washington, a calculation that appeared to have made him popular with millions who felt they had not benefited from their government's close ties to Iran or the United States.

Sadr called for the departure of the remaining 2,500 U.S. troops and told Tehran he would "not leave Iraq in its grip".

Iraq has been a proxy battlefield for influence between the United States and Iran since the U.S.-led invasion, which toppled Saddam and created a path to power for a Shi'ite majority led by figures courted for decades by Tehran.

Most of Iraq's Shi'ite political establishment remains suspicious or even hostile to Sadr. Still, Sadr's political organisation, the Sadrist movement, has come to dominate the apparatus of the Iraqi state since the 2018 poll, taking senior jobs within the interior, defence and communications ministries.

The former insurgent's movement swept parliamentary elections in 2021, coming first and increasing the number of seats he holds in the 329-seat parliament to 73 from 54.

The victory dealt a crushing blow to pro-Iranian Shi'ite groups whose parliamentary representation collapsed.

Sadr proclaimed the result a "victory by the people over ... militias". His supporters were elated.

At least one pro-Iran militia commander said the armed groups were prepared to use violence if necessary to ensure they did not lose influence after what they saw as fraudulent polls.

Sadrist politician Hussein al-Aqabi said Sadr's policy of not relying on the United States or Iran paid off, in contrast to parties reliant on regional powers which "ended up almost in the shadows."