The leader of radical Sunni fighters who have made rapid military advances in Iraq is the rising star of global jihad, driven, Islamist fighters say, by an unbending determination to fight for and establish a hard-line Islamic state.

Abu Bakr al-Baghdadi, commander of the Islamic State in Iraq and Syria (ISIS), now controls large parts of eastern Syria and western Iraq, a vast cross-border haven for militants in the Sunni Muslim core of the Middle East.

Despite his power — and a $10 million reward offered by the U.S. for information leading to his capture — little is known about a man who for his own survival has shunned the spotlight.

Fighters from ISIS and its rivals praised al-Baghdadi as a strategist who succeeded in exploiting turmoil in Syria and Iraq’s weak central authority after the U.S. military withdrawal to carve out his power base.

He has proved ruthless in eliminating opponents and showed no hesitation in turning against former allies to further his ambition of creating an Islamist state.

Enemies, even those from rival radical groups who broadly share ISIS’s religious ideology, are fought and defeated. Captured fighters — and noncombatants — are usually shot or decapitated, their deaths recorded in grisly videos that inspire fear and revulsion among opponents.

“In short, for Sheik al-Baghdadi, each religion has its state except Islam, and it should have a state and it should be imposed. It is very simple,” one of his non-Syrian members said from inside Syria.

According to the U.S. reward notice, al-Baghdadi was born in the Iraqi town of Samarra in 1971. He received a doctorate in Islamic studies at Baghdad University, jihadi websites say, and after years of fighting with al-Qaida groups became leader of its Iraq branch in 2010.

A year later, sensing opportunity when the uprising against Syrian President Bashar Assad erupted, al-Baghdadi sent an aide across the border to expand al-Qaida’s foothold there.

That aide, Abu Mohammad al-Golani, set up al-Qaida’s Jabhat al-Nusra, which quickly rose to prominence with a series of deadly car bombings. It also earned a reputation as the most effective of the many disparate forces fighting Assad.

But as al-Golani grew strong in Syria and rejected an edict to merge his forces under al-Baghdadi’s command, al-Baghdadi launched a war against al-Nusra, leading to a split with al-Qaida leader Ayman al-Zawahri.

For many of al-Baghdadi’s supporters the clash between their battlefield commander and the nominal but distant al-Qaida leader, who tried in vain to impose his authority to end the dispute, was no surprise.

When al-Qaida founder Osama bin Laden was killed by U.S. forces in Pakistan three years ago, al-Baghdadi “was the only one who did not pledge allegiance to al-Zawahri,” the non-Syrian ISIS member said. “He was assigned by Sheik Osama to establish the state, this was his plan before he (bin Laden) was killed.”

While al-Baghdadi’s supporters believe an Islamic state will revive the glories of Islam under the Prophet Muhammad, they say al-Zawahri feared that by drawing jihadi fighters together in one place it would make it easier for the West to defeat them.

Ignoring al-Zawahri’s calls to leave Syria to Jabhat al-Nusra, al-Baghdadi expanded operations across northern and eastern parts of Syria in 2012 and 2013, sometimes battling Assad’s forces but more often pushing out other rebel fighters.

ISIS’s unforgiving treatment of ordinary Syrians won it many enemies and by the end of last year an alliance of al-Nusra and other Islamist brigades struck back, pushing ISIS back to its stronghold along the Euphrates River in the oil-producing deserts of eastern Syria.

But ISIS has grown stronger, not weaker. Al-Baghdadi’s fighters control the city of Raqqa — Syria’s only provincial capital completely beyond Assad’s control — and have imposed strict Islamic law.

In neighboring Deir al-Zor province ISIS has waged a six-week offensive against rival rebels, seizing oil fields and towns on the northeast bank of the Euphrates 100 km from the Iraqi border.

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, al-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.

Al-Baghdadi’s real and very visible strength stands in sharp contrast to al-Zawahri, in hiding for more than a decade and trying to influence a global jihad most of which is played out far away.

Even al-Baghdadi’s rivals say the ISIS 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 an al-Nusra fighter from the Syrian city of Aleppo, adding bitterly that al-Baghdadi’s supporters “cannot see the damage he is inflicting.”

From al-Nusra’s perspective, Islamists in Syria have “entered a cycle of blood and nobody will come out of it,” he added.

To his followers, al-Baghdadi represents a new generation of fighters working to fulfill the next stage of bin Laden’s dream, moving from al-Qaida — which can mean “base” in Arabic — toward the fully fledged radical state.

“Sheik al-Baghdadi and Sheik Osama are similar. They always look ahead, they both seek an Islamic state,” said a Syrian ISIS fighter.

Others go further, saying al-Baghdadi’s creation of ISIS makes al-Zawahri’s part of al-Qaida’s operation redundant.

“The group al-Qaida does not exist any more. It was formed as a ‘qaida’ (base) for the Islamic state and now we have it, al-Zawahri should pledge allegiance to Sheik al-Baghdadi,” said the non-Syrian ISIS fighter.

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

Among his strategies, al-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 al-Baghdadi outside the Middle East.

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

In a sign of their brutality, a video posted on the Internet shows ISIS 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 al-Baghdadi’s men operate by a simpler rule: Whoever stands in their way should be terminated, regardless of religion or sect.

Asked how serious al-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 al-Baghdadi then they are fools, they do not know what will hit them in the future.”