As its feared and fearsome leader, Abu Bakr al-Baghdadi personifies the brutality, determination and ambition of the Islamic State of Iraq and the Levant.
Not since Osama bin Laden has a leader been held in such reverence among Sunni fighters, scored such stunning and shocking victories, and threatened so much of the established order.
But unlike Bin Laden, whose vast wealth aided his elevation to the "sheikh", Baghdadi has literally fought his way from ordinary beginnings in northern Iraq to lead what is perhaps the Middle East’s most feared irregular armed force.
So emboldened by his success on the battlefields of Syria and Iraq, Baghdadi has challenged the very leadership of al-Qaeda, denouncing them publicly as deviating from the cause and stating he is the true heir to Bin Laden's legacy.
| Abu Bakr al-Baghdadi
But his methods are extreme and his actions repugnant to many - captured enemy fighters are shot or decapitated and their deaths recorded for the internet.
Other armed groups in Syria are attacked as ISIL expands territory and influence, and a strict interpretation of Islam is implemented in the regions under its control - internet videos abound of thieves having their hands severed and adulterers, smokers and those who fail to attend prayer being publicly whipped.
Little of Baghdadi’s early life is on record. It is known that he was born Awwad Ibrahim al-Badri al-Samarri to a religious family in Samarra in 1971. He studied Islamic history as a student and, according to sympathetic websites, gained a doctorate from Baghdad university in the late 1990s.
It is likely Baghdadi held a religious position in the Sunni community when the US invaded Iraq in 2003.
Like many enraged by the invasion, he became involved in the armed rebellion and began fighting in western Iraq, possibly Anbar - the stronghold of Tawhid and Jihad led by the Jordanian, Abu Musab al-Zarqawi, who later rebranded the group al-Qaeda in Iraq.
But Baghdadi's resistance was cut short in about 2006, when he was arrested by US forces and held in Camp Bucca, the main US-run prison in Iraq following the torture scandal and shutdown of Abu Ghraib.
Such was his relative anonymity, it seems, that Baghdadi was interred as a low-level prisoner. And it is here, analysts believe, that he became more deeply involved with fighters from al-Qaeda.
After his release in the late 2000s, he joined and fought with the Islamic State of Iraq, known as ISI, the successor group to al-Qaeda in Iraq. With its ranks swollen by foreign and Iraqi fighters, the group was the dominent Sunni force in the country, attacking and intimidating its US and sectarian enemies with suicide bombings, abductions and murder.
Perhaps as a sign of things to come, ISI was publicly reprimanded by al-Qaeda for its brutality and its willingness to kill anyone, even Sunni Muslims, it considered betrayers of their religion.
Some reports say Baghdadi held sway over his own religious court, pronouncing - often without mercy - on the fate of those before him. Others say he played a key role in smuggling foreign fighters into Iraq.
He quickly climbed the ranks, earning a place on the organisation's ruling council before being declared leader in 2010 after his predecessor, Abu Omar al-Baghdadi, was killed by US and Iraqi forces.
It was the outbreak of the Syrian war that presented Baghdadi with the opportunity to expand his cause. He sent a lieutenant, Abu Mohammed al-Joulani, to create the Nusra Front and fight the Assad regime.
From there, his rise gathered pace and he declared in 2013 the takeover of Nusra to add the Levant to the Islamic State of Iraq. Baghdadi moved to Syria and ignored pronouncements by the leader of al-Qaeda, Ayman al-Zawarhiri, that the merger with Nusra was invalid.
|ISIL holds areas of Iraq and Syria
That schism deepened in April of this year, when the ISIL declared that "al-Qaeda is no longer the base of jihad... its leadership has become a hammer to break the project of the Islamic state... al-Qaeda's leaders have deviated from the correct paths".
Baghdadi's interpretation of Islam has been enforced in the group's stronghold of Raqqa, in northern Syria; capital and corporal punishment for a range of crimes, public floggings, mandatory prayer and reports of a Christian being crucified to send a message to his community.
So how did an Islamic scholar from Samarra become the most feared radical fighter in the Middle East, prepared to disregard al-Qaeda's "old guard" and declare himself the new force?
Apart from in Syria since 2013, there is no evidence that Baghdadi has ever fought abroad, like many of his peers. At the time of his arrest by US forces he was not considered a big catch.
Events, it seems, have shaped the man, and compelled him to shape his strategy. Baghdadi supporters speak of him as al-Qaeda mark two, the leader of a new generation working to bring about the Islamic caliphate envisoned by Bin Laden.
"Sheikh Baghdadi and Sheikh Osama are similar. They always look ahead, they both seek an Islamic state," a Syrian ISIL fighter told the Reuters news agency.
A non Syrian fighter told the agency: "The group al-Qaeda does not exist any more. It was formed as a base for the Islamic state and now we have it, Zawahiri should pledge allegiance to Sheikh Baghdadi."
Charles Lister, a visiting fellow at the Brookings Doha Centre, told Al Jazeera: "There can be no doubt ISIL’s rise in recent years is due to Baghdadi’s shaping it into a transnationally-minded and brutal organisation.
"Baghdadi has presented himself as a preeminent jihadist leader of the 21st century, and by extension, certainly a competitor and rival to Zawahiri."
Lister, who has written extensively on Syria, said that the escalation of the Syrian conflict since mid-2011 aided Baghdadi's successful recovery of the ISI and his expansion into Syria with ISIL.
"The sectarian element within the Syrian conflict contributed towards enhancing the principle theme used by Baghdadi to justify his fight against Baghdad.
Al-Qaeda does not exist any more. Zawahiri should pledge allegiance to Sheikh Baghdadi.
"ISIL’s involvement in Syria and the controversy developed over its role in that conflict also, by extension, brought more and more attention to the conflict in Iraq, which appears to have encouraged increased levels of foreign fighter recruitment in Iraq also.
"ISIL's extensive and slick PR apparatus and its bold mode of operation has undoubtedly lent it real clout within the international jihadist community. These latest gains in Iraq will have served to consolidate that status.
"A common theme among European members of ISIL is that Baghdadi represents a continuation of the ideals expounded by Bin Laden and that Zawahiri has failed to continue that line."
The ISIL's latest gains in Iraq are the result. Reports suggest the ISIL has plundered $425m from banks in northern Iraq, and looted the stores and equipment from Iraq army bases left undefended by fleeing troops.
"ISIL’s operations in Iraq and Syria are intricately linked together within a single strategy, with activities in one country often feeding off momentum in the other," said Lister.
"This major push in Iraq has been long in the coming and the gains made - particularly in terms of weaponry and money - will undoubtedly bolster ISIL’s capacity to push back against rival forces in Syria, potentially even leading the group to move back into the northern governorates of Idlib, Latakia and western Aleppo."
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