On the face of it, U.S. claims the Iranians plotted to assassinate Saudi Arabia's ambassador in Washington seem far-fetched and nothing less than a declaration of war on Tehran's longtime rival for leadership of the Muslim world.

The two Persian Gulf titans are locked in a regional cold war that has long involved clandestine operations by both sides.

But if the allegations that the Iran's al-Quds Force, the covert action arm of the elite and powerful Revolutionary Guards, are correct, then the plot takes on an altogether different hue.

That's because the shadowy figure who commands the al-Quds Force, Brig. Gen. Qassem Suleimani, has racked up a string of successful "black operations" doing Tehran's dirty work.

Until quite recently, little was known about Suleimani, who has long been the invisible man in Iran's intelligence hierarchy and an enigma to the U.S. intelligence community that's one of his main adversaries.

He's hailed as a national hero in Iran but, apart from a couple of brief television appearances, in recent years he's rarely been seen in public.

Until recently the Americans and their allies knew little about him.

But these days, he and his force, whose strength is estimated at between 1,000 and 15,000, have become the deadly spearhead of Shiite Iran's foreign policy across the mostly Sunni Middle East and Central Asia.

Suleimani turned Iraq into a quagmire of Iranian covert operations against the Americans in 2005 using Iraqi Shiite "Special Groups" funded, trained and armed by al-Quds.

These days nothing happens in Iraq without Suleimani's say-so and the Special Groups are his muscle.

Martin Chulov of The Guardian daily in London, who spent a lot of time in Iraq, recounts how when he mentioned Suleimani's name during an interview with Iraq's intelligence chief, Sharwan al-Waeli, the man's hand trembled.

"You mean Sayyed Qassem Suleimani," Waeli said, giving the Iranian an Arabic honorific usually reserved for male descendants of the Prophet Mohammed through his grandsons.

"In Baghdad, no other name invokes that sort reaction among the nation's power base -- discomfort, uncertainty and fear," Chulov wrote.

Former CIA officer Philip Giraldi, who spent years operating undercover in the Middle East in the 1980s when Iran was conducting constant "black operations" across the region, recalls that although Suleimani was involved in these spying and assassination missions he was "pretty much unknown to US intelligence."

Giraldi said there was a file on the general at CIA headquarters, at that time, "but it was pretty much empty."

These days, the Americans have come to appreciate how dangerous Suleimani is and how crucial a role he plays in Iran's growing power in the Middle East and its environs.

The U.S. Treasury Department has branded him a terrorist, along with his entire command.

In March 2008, Suleimani brokered a truce in a major battle in the southern Iraqi city of Basra, near the country's main oilfields, between the Mehdi Army, the militia of firebrand Shiite cleric Moqtada Sadr, and the security forces of the Shiite-dominated Baghdad government of Prime Minister Nouri al-Maliki that was in danger of escalating into a full-scale civil war.

Suleimani's success underlined the authority and power he wields in the notoriously opaque Tehran regime and in Iraq.

More importantly, his actions illustrate how this perplexing figure is so adept at meshing covert operations with strategic diplomacy.

The al-Quds Force is responsible for all Tehran's clandestine operations abroad.

Suleimani, says Washington Post columnist David Ignatius, "represents the sharp point of the Iranian spear … He's also Iran's leading strategist on foreign policy."

After Shah Mohammad Reza Pahlavi was toppled in the Islamic Revolution in 1979, Suleimani joined the Revolutionary Guards, formed to protect the new fundamentalist regime.

He distinguished himself in combat during the 1980-88 war against Iraq, and wound up commanding the Guards' 41st Tharallah Division. He reportedly headed covert operations in Bosnia during the Balkan wars of the 1990s and in 1996 was operating in Afghanistan.

These days, Suleimani effectively runs Hezbollah in Lebanon, Iran's most prized proxy, and has becomes a key figure helping the Syrian regime, Iran's key Arab ally, suppress a stubborn 6-month-old uprising.

If Suleimani was involved in the alleged plot to kill Saudi Ambassador Adel al-Jubeir then the omens are bad, because he reports directly to Ayatollah Ali Khamenei, Iran's supreme leader.