But several still cautioned that, while his death was a significant development, it wouldn't end the terror operations or violence in Iraq.
The death shouldn't cause anyone to have unrealistic expectations, said one official, who requested anonymity while details of Zarqawi's death were still unfolding.
The impact of Zarqawi's death is nonetheless symbolic: The U.S. has not seen the elimination of such an iconic figure since former President Saddam Hussein was found in an underground bunker in late 2003.
Zarqawi was considered the most dangerous terror plotter and foreign fighter in Iraq, coordinating a loose coalition of militants numbering at least in the hundreds. Usama bin Laden called him the "emir," or prince, of Al Qaeda in Iraq.
The U.S. government was offering up to $25 million for information leading to Zarqawi's killing or capture, putting him on par with Hussein, bin Laden and his top deputy, Ayman al-Zawahiri.
During a speech in April, Gen. Michael Hayden, the newly appointed CIA director who was then serving as the No. 2 U.S. intelligence official, said the war in Iraq motivates jihadists, but their failure there would weaken the movement globally.
"The loss of key leaders like bin Laden, Zawahiri and Zarqawi — especially if they were lost in rapid succession — could cause the jihadist movement to fracture even more into smaller groups, and would probably lead to strains and disagreements," Hayden said.
Al Qaeda in Iraq has taken responsibility for numerous mortar attacks, suicide bombings, beheadings and other violence against U.S. and Iraqi targets. Scores, including many ordinary Iraqis, have died.
Yet even into 2004, Zarqawi was considered a shadowy figure whose followers were known simply as "the Zarqawi network." He operated under the names of various jihadist groups, and began emulating bin Laden with recordings fraught with anti-Western rhetoric and calls to arms.
U.S. intelligence veterans have said he craved attention and saw an expanded role for himself in the Al Qaeda organization.
But the U.S. government has misunderstood him at times.
The Bush administration cited Zarqawi's presence in Iraq before the April 2003 collapse of Saddam's government among its evidence of contacts between Al Qaeda and the former regime — and part of its justification for the Iraq war.
While Zarqawi is believed to have been in Iraq, he was not operating as part of Al Qaeda then. The July 2004 report from the Sept. 11 Commission found no evidence of a collaborative relationship between Saddam and bin Laden's terror organization before the invasion.
But by October 2004, Zarqawi pledged his allegiance to bin Laden.
Zarqawi was also known for a time as the "one-legged terrorist," because U.S. authorities believed was fitted for an artificial leg in Baghdad in 2002. The assessment was later revised.
Over time, a more vivid picture of Zarqawi emerged.
Born in Jordan in 1966, Zarqawi developed ties to mujahedeen, or holy warriors, while fighting alongside them during the Soviet invasion of Afghanistan in the 1980s.
Intelligence officials believe Zarqawi has cells or links to Muslim extremists worldwide, including Iraq, Afghanistan, Turkey, Spain, Saudi Arabia, Sudan, Syria, Pakistan and Kuwait.
In the United States, FBI and other government officials did not believe Zarqawi had operatives under his command, but they had said it's likely that he had ties to some U.S.-based militants or sympathizers from his years of work in the extremist community.
U.S. officials have said bin Laden contacted Zarqawi last year to enlist him in attacks outside Iraq. Zarqawi's group claimed responsibility for deadly bombings at three hotels in Jordan in November, including a wedding, which drew fierce condemnation.
At a rally, hundreds of angry Jordanians shouted "Burn in hell, Abu Musab al-Zarqawi!" after the terrorist's group claimed responsibility for the blasts.