Age: 37
Occupation: Iraqi Shi'ite cleric
Previous TIME 100 appearances: 2
His political movement is the make-or-break member of Iraq's coalition government. Al-Sadr's triumphant return after nearly four years of self-imposed exile in Iran suggests he wants a hands-on role in Iraqi affairs. This is bad news for the U.S.: al-Sadr was vehemently anti-American even before he came under Tehran's protection. His militia, the Mahdi Army, has been blamed for sectarian violence that has killed tens of thousands of Iraqis.