Profile of Abu Bakr al-Baghdadi, the newly appointed 'Caliph' of 'all Muslims'

Abu Bakr al-Baghdadi, the shadowy jihadist fighting in Iraq and Syria, and newly declared leader of a "caliphate" encompassing all Muslims, is increasingly seen as more powerful than Al-Qaeda's chief.

The leader of the powerful Islamic State of Iraq and the Levant (ISIL) militant group was declared Sunday the "caliph" in an attempt to revive a system of rule that ended nearly 100 years ago with the fall of the Ottoman Empire.

"The Shura (council) of the Islamic State met and discussed this issue (of the caliphate)... The Islamic State decided to establish an Islamic caliphate and to designate a caliph for the state of the Muslims," ISIL spokesman Abu Mohammad al-Adnani said in an audio recording distributed online.

"The jihadist cleric Baghdadi was designated the caliph of the Muslims," said Adnani.

Baghdadi, born in Samarra in 1971 according to Washington, apparently joined the insurgency that erupted shortly after the 2003 US-led invasion of Iraq, at one point spending time in an American military prison in the country.

In October 2005, American forces said they believed they had killed "Abu Dua," one of Baghdadi's known aliases, in a strike on the Iraq-Syria border.

But that appears to have been incorrect, as he took the reins of what was then known as the Islamic State of Iraq (ISI) in May 2010 after two of its chiefs were killed in a US-Iraqi raid.

Since then, details about him have slowly trickled out.

In October 2011, the US Treasury designated him as a "terrorist", and this year, Iraq released a picture they said was of Baghdadi, the first from an official source, depicting a balding, bearded man in a suit and tie.

US officials said last year that the jihadist was likely in Syria, but information of his whereabouts since has been unclear.

Late last month, Lieutenant General Abdulamir al-Zaidi, who heads a northern security command centre, said his forces believed Baghdadi was inside Iraq, but other officials have contested this.

He is touted within ISIL as a battlefield commander and tactician, a crucial distinction compared with Al-Qaeda chief Ayman al-Zawahiri, has attracted legions of foreign fighters, with estimates pegging them in the thousands.

At the time Baghdadi took over the group in April 2010, when it was ISI and tied to Al-Qaeda, it appeared to be on the ropes, after the "surge" of US forces combined with the shifting allegiances of Sunni tribesmen to deal him a blow.

But the group has bounced back, expanding into Syria in 2013.

Baghdadi sought to merge with Al-Qaeda's Syrian franchise, Al-Nusra Front, which rejected the deal, and the two groups have mostly operated separately since.