Who is Moqtada al-Sadr? Iraq’s leading insurgent and scion of one of the country’s leading religious dynasties. The 35-year-old is a poor public speaker but holds enormous influence over mainly poor Shiites in Baghdad and Basra. He is regarded by America as public enemy no. 1 in Iraq. Mr. Sadr’s newspaper was banned in 2004 for spreading hatred and a warrant for his arrest was issued. American marines fought Mr. Sadr’s followers for control of Najaf the same year. Mr. Sadr’s Mahdi army is the most powerful grassroots organization in Iraq.

How the Mahdi army is viewed in Iraq depends where one stands on the sectarian divide. The Mahdi army spearheaded the worst fighting of Iraq’s civil war. Its fighters now dominate eastern Baghdad and swathes of its western districts, areas which have been cleansed of Sunni Muslims.

Elsewhere, Mr. Sadr generally gets credit for being the most nationalistic of Iraqi leaders. Despite declaring a ceasefire against American and British troops last August, he remains an implacable foe of the presence of foreign troops in Iraq. The American commander in Iraq, General David Petraeus, recognized that the ceasefire could dramatically curtail American military casualties. American spokesmen were instructed to draw the distinction between “responsible” followers of Mr. Sadr, who suspended fighting, and “Special Groups” of Shiite guerrillas, who continued the insurgency.

Mr. Sadr is believed to have moved to Tehran last year and is studying to become an ayatollah in the holy city of Qom. He is said to have married an Iranian woman. The best that can be hoped for is that Sadr supporters will acquiesce to a stronger security force and establish their support in provincial elections, due to be held in October.