Kneeling in the second row on the mosque’s carpeted floor was Major General Qassem Suleimani, the Quds Force’s leader: a small man of fifty-six, with silver hair, a close-cropped beard, and a look of intense self-containment. It was Suleimani who had sent Shateri, an old and trusted friend, to his death. As Revolutionary Guard commanders, he and Shateri belonged to a small fraternity formed during the Sacred Defense, the name given to the Iran-Iraq War, which lasted from 1980 to 1988 and left as many as a million people dead. It was a catastrophic fight, but for Iran it was the beginning of a three-decade project to build a Shiite sphere of influence, stretching across Iraq and Syria to the Mediterranean. Along with its allies in Syria and Lebanon, Iran forms an Axis of Resistance, arrayed against the region’s dominant Sunni powers and the West. In Syria, the project hung in the balance, and Suleimani was mounting a desperate fight, even if the price of victory was a sectarian conflict that engulfed the region for years.

Suleimani took command of the Quds Force fifteen years ago, and in that time he has sought to reshape the Middle East in Iran’s favor, working as a power broker and as a military force: assassinating rivals, arming allies, and, for most of a decade, directing a network of militant groups that killed hundreds of Americans in Iraq. The U.S. Department of the Treasury has sanctioned Suleimani for his role in supporting the Assad regime, and for abetting terrorism. And yet he has remained mostly invisible to the outside world, even as he runs agents and directs operations. “Suleimani is the single most powerful operative in the Middle East today,” John Maguire, a former C.I.A. officer in Iraq, told me, “and no one’s ever heard of him.”