The world first heard of Abu Musab al-Zarqawi on Feb. 5, 2003. That was the day that then U.S. Secretary of State Colin Powell went to the United Nations to make the case for the invasion of Iraq. “Iraq today harbors a deadly terrorist network, headed by Abu Musab al-Zarqawi, an associate and collaborator of Osama bin Laden and his al Qaeda lieutenants,” Powell told the U.N. Security Council. That information, we now know, was false. But it laid ground to one of the most powerful and enduring myths of the war on terror—the myth of Abu Musab al-Zarqawi.

That Zarqawi and bin Laden would be mentioned in the same breath—and from an official as senior as Powell—probably shocked no one more than Zarqawi. There are, after all, hundreds of men just like him throughout the Arab world, committed jihadists with some penchant for leading others. Although Zarqawi had demonstrated a zeal for his cause, there was little about him to suggest that he would catapult to the top ranks of the world’s deadliest terrorists. Uneducated and from a poor, working-class family, Zarqawi lacked the pedigree, connections, and financing that marked bin Laden and other senior leaders of al Qaeda.

But, of course, Zarqawi is no longer a mere foot soldier. From New York to London, from Paris to Tokyo, Zarqawi has become the new face of Islamic terror. He has replaced Saddam Hussein as the poster boy of evil in the Arab world. He commands a cadre of Iraqi insurgents that have purportedly carried out many of the barbarous terrorist attacks in that country since the ousting of Saddam. Now with a $25 million bounty on his head, this high school dropout from the slums of Jordan has tied the United States down in its deadliest conflict since the Vietnam War.

But how did myth become reality? Prior to Sept. 11, 2001, the U.S. government had never...