Islamic State leader and the world’s most wanted man Abu Bakr al-Baghdadi has been killed in a US military operation in northwest Syria. But who was the notorious terrorist? Here’s what you need to know.

Abu Bakr al-Baghdadi was the nom de guerre of the infamous mastermind of the barbaric so-called Islamic State (ISIS, formerly ISIL) terror group. Followers of the group called him Caliph Ibrahim and he had a range of other names including Sheikh Baghdadi and Al-Shabah, meaning ‘the ghost’.

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Mystery surrounds many aspects of the Iraqi native’s life but he was believed to be 48-years-old and hailed from near the city of Samarra, 125km north of Baghdad, and was part of the al-Bu Badri tribe.

This tribal link allowed Baghdadi to claim that he was a descendant of the Prophet Muhammad's Quraysh tribe, a neccessary qualification for becoming the caliph (the historic leader of all Muslims).

The US invasion of Iraq prompted Baghdadi and his associates to create Jaysh Ahl al-Sunnah wa-l-Jamaah (the Army of the Sunni People Group) which operated around Samarra, Diyala and Baghdad and later declared an oath of allegiance to Al Qaeda.

He was picked up by US-led coalition forces and detained from February to December 2004, but was released as he was not considered a high-level threat.

The group changed its name to the Islamic State of Iraq (ISI) in 2006 and Baghdadi was appointed the general supervisor of the sharia committees for the “state’s” provinces.

Following the death of ISI leader Abu Umar al-Baghdadi in April 2010, he became the head of the organization and took credit for a blitz of suicide bombings and other attacks targeting Shia and moderate Sunni Muslims that left thousands dead between 2010-2013.

Baghdadi broke the group away from Al Qaeda and declared his own, more aggressive jihadist group. In 2014, the so-called Islamic State overran large swathes of Iraq and Syria and Baghdadi appeared in an infamous video at the al-Nuri mosque in Mosul, Iraq, where he announced a "caliphate" in the regions they controlled.

During the height of its rule, the group enforced its barbarous version of Islamic law on millions. It has been blamed for mass executions and is accused of carrying out war crimes.

Rumors of Baghdadi’s demise have long circulated. After declaring the creation of the ‘caliphate’ in 2014, he seemingly vanished for years, prompting rampant speculation that he had been killed.

He remained unseen as the so-called caliphate swelled to an area roughly the size of Britain and remained in the shadows as the terror group was fought back by a multinational effort led by Syria, Russia and Iran, as well as a coalition led by the US.

Then, after five years without an appearance, he suddenly reemerged in April this year, when footage of him discussing jihad with his cohorts was released. The video shows Baghdadi claiming that the Easter bombings in Sri Lanka were “revenge” for battles lost in Syria.

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The reappearance was largely interpreted as a reassertion of his leadership of the group that, while on the backfoot in its own backyard, had claimed several deadly attacks in Europe.

As recently as September, the group released an audio message said to be from Baghdadi which praised the operations of IS affiliates in other regions.

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