Previous American administrations had resisted striking General Suleimani directly, either because of operational concerns or out of fear that killing him could destabilize the region further and lead to all-out war between the United States and Iran.

At least once, though, Israeli officials ran the possibility of attacking him up their command structure. That was in February 2008, while Israeli and American intelligence operatives were tracking Mr. Mugniyah, the Hezbollah commander, in the hopes of killing him, according to senior American and Israeli intelligence officials. Operatives spotted the Hezbollah commander talking with another man, who they quickly determined was Mr. Suleimani.

Excited by the possibility of killing two archenemies at once, the Israelis phoned senior government officials. But Prime Minister Ehud Olmert denied the request, as he had promised the Americans that only Mr. Mugniyah would be targeted in the operation.

Perhaps more than any other individual, General Suleimani was the foil for American plans in Iraq, which like Iran is predominantly Shiite.

After the United States invaded Iraq in 2003, Iranian militiamen and their Iraqi allies fought a clandestine war against American troops, launching rockets at bases and attacking convoys. The militias also played a large part in inflaming sectarian tensions that led to Iraq’s civil war in 2006 and 2007 between Shiites and Sunnis, leading President George W. Bush to order a troop surge there.

General Suleimani and other leaders of his generation were shaped by the brutal war between Iran and Iraq in the 1980s, a conflict so cruel, with trench warfare and chemical weapons, that some compared it to the devastation of World War I. Nearly a million people died on both sides, and General Suleimani spent much of that war on the front lines.