Al-Sadr is the thirtysomething heir to a religious dynasty. His grandfather's picture is pasted all over the Shiite neighborhood in Baghdad that bears the family name: Sadr City.
Today, thousands of his followers marched to commemorate the murder in 1999 of al-Sadr's father, a grand ayatollah, by Saddam Hussein's assassins.
Muqtada al-Sadr himself has only basic religious training. He is married, but childless, and keeps his private life away from the camera. But he flaunts his ferociously anti-American message, which boils down to "Get your troops out."
But it's not only that message that appeals to many of Iraq's Shiite majority, many of whom are poor and powerless. When bombs in Sadr City killed more than 200 people last Thursday, al-Sadr's organization raced to the rescue with first aid, crowd control, and the next day, compensation.
But there's a darker side to al-Sadr's loyalists. They've taken over important government ministries and infiltrated the U.S-trained Iraqi police. His gunmen are also said to run the death squads that torture and murder Sunnis.
Al-Sadr has also consolidated his power in Iraq's parliament. His loyalists occupy the 30 crucial seats that give Prime Minister al-Maliki his majority. But to consider what it all adds up to, consider this: When American forces encircled Sadr City a few weeks ago to look for a kidnapped U.S. soldier, al-Sadr called a meeting with the prime minister. The very next day, U.S. forces were ordered to leave Sadr City.