Who is al-Baghdadi...

Oil sold on the black market provides millions of dollars in revenues, rebels say. Combined with Iraqi recruits and the military equipment seized in his capture of the Iraqi city of Mosul, Baghdadi now has a formidable array of resources.

Supporters say that is key to achieving his aim of military self- sufficiency, ensuring an independent flow of money, manpower, weapons and energy supplies.

Rival to Zawahri

Baghdadi's real and very visible strength stands in sharp contrast to Zawahri, in hiding for more than a decade and trying to influence a global jihad most of which is played out a long way from his refuge.

Even Baghdadi's rivals say the ISIL leader is in the ascendancy, winning influence well beyond Syria and Iraq.

"He is becoming very popular among jihadis. They see him as someone who is fighting the war of Islam," said a Nusra Front fighter from the Syrian city of Aleppo, adding bitterly that Baghdadi's supporters "cannot see the damage he is inflicting".

"He has received letters expressing loyalty from Afghanistan and Pakistan as well," the Nusra fighter said. "Sheikh Zawahri is trying but I think it is too late."

From Nusra's perspective, Islamists in Syria have "entered a cycle of blood and nobody will come out of it," he added.

To his followers, Baghdadi represents a new generation of fighters working to fulfil the next stage of bin Laden's dream, moving from Qaeda - which can mean 'base' in Arabic - towards the fully fledged radical state.

"Sheikh Baghdadi and Sheikh Osama are similar. They always look ahead, they both seek an Islamic state," said a Syrian ISIL fighter.

Others go further, saying Baghdadi's creation of ISIL makes Zawahri's part of al Qaeda's operation redundant.

"The group al Qaeda does not exist any more. It was formed as a qaeda (base) for the Islamic State and now we have it, Zawahri should pledge allegiance to Sheikh Baghdadi," said the non- Syrian ISIL fighter.

Another jihadi who described himself as close to Baghdadi said Zawahri was watching, powerless, to see whether the ISIL leader makes a false move. "He is waiting to see if Baghdadi will win or fall, but in either case he is no longer leader."

World should fear him

Among his strategies, Baghdadi has opened the door to foreign fighters, particularly Europeans and Americans, providing them with training and a sense of purpose.

While they are useful on the Syrian battlefield, they may also head back home one day, war veterans with experience to recruit others to carry out attacks for Baghdadi outside the Middle East.

They are trained to be fearless and merciless. Activists in several areas inside Syria say that Baghdadi's men walk around wearing explosive vests.

In a sign of their brutality, a video posted on the internet shows ISIL fighters, some of whom do not appear to speak Arabic, executing several men. Two victims were reciting the Shahada, the Muslim declaration of faith, as they were killed.

Many clerics say it is forbidden to kill a person while they declare the Shahada, but Baghdadi's men operate by a simpler rule: whoever stands in their way should be terminated, regardless of religion or sect.

Asked how serious Baghdadi is, a supporter replied: "When you have his army, his determination and his belief then the world should fear you."

"If the world does not fear Baghdadi then they are fools, they do not know what will hit them in the future."