Discreet in his youth and invisible as the world's most wanted man, Abu Bakr al-Baghdadi rose through the ranks quietly and patiently to become global jihad's undisputed supremo.
The Russian army said Friday that Baghdadi may have been killed in a May 28 air strike near the jihadists' Syria stronghold of Raqa, although there was no immediate confirmation from his Islamic |State group or the US-led coalition battling IS in Syria and Iraq.
The 46-year-old Iraqi-born leader of the IS, nicknamed "The Ghost", has not been seen in public since he proclaimed himself "caliph" in the Iraqi city of Mosul three years ago.
The fortunes of his "caliphate" have since turned -- with massive simultaneous offensives by allied forces against both Mosul and Raqa.
The world's most-wanted man has been rumoured wounded or killed a number of times in the past.
The last sign of life he gave was in November last year after Iraqi forces supported by the aerial might of the coalition launched their reconquest of Mosul, the country's second city.
In an audio recording, he urged his men to defend Mosul to the bitter end and Iraqi elite forces have gained huge ground but are still battling die-hard jihadists around the Old City.
Baghdadi was said to have left Mosul earlier this year and has since been reportedly spotted in various areas near the Syrian-Iraqi border.
But his whereabouts were never confirmed.
"It is rather remarkable that the leader of the most image-conscious terrorist group is so low-key in terms of his own publicity," said Patrick Skinner, an analyst with the Soufan Group intelligence consultancy and a former CIA case officer.
That low profile -- a perfect antithesis to Osama bin Laden -- is partly what Baghdadi, who has a $25-million US bounty on his head, has owed his rise as well as his survival to.
The man who in 2014 became the overlord of a jihadist state ruling over millions of inhabitants was born Ibrahim Awad al-Badri to a modest family in Samarra, north of Baghdad.
An introvert, he was mostly known locally for his skills as a footballer, a sport his group would later target as a product of the Western society jihadists claim to despise.
Baghdadi's high school results were too modest to undertake a law degree and his eyesight too bad to join the army so he moved to the capital to study Islam, settling in the neighbourhood of Tobchi.
"He comes across as someone who was never brilliant but was patient and hard-working," said Sofia Amara, author of a recently-released documentary that unveiled exclusive documents on Baghdadi.
"He had a vision, early on, of where he wanted to go and what kind of organisation he wanted to create," she said. "He is a secret planner."
After US-led forces invaded Iraq in 2003, he founded his own insurgent outfit.
It never carried out major attacks, however, and by the time he was arrested in February 2004 and detained at the Camp Bucca facility, he was still very much a second or third-tier jihadist.
The US prison in southern Iraq, which was later dubbed "the University of Jihad", was where he became radicalised and started showing signs of the leader he is now.
"People there realised that this nobody, this shy guy was an astute strategist," Amara said.
He was released at the end of 2004 for lack of evidence. Iraqi security services arrested him twice subsequently, in 2007 and 2012, but let him go because they did not know who he was.
In 2005, after his release from Bucca, he pledged allegiance to Abu Musab al-Zarqawi, the brutal leader of one of IS's many previous incarnations.
Zarqawi was killed in 2006 and Baghdadi took over from his successor, who was also eliminated, in 2010.
He revived the fortunes of Iraq's struggling Al-Qaeda affiliate, the Islamic State of Iraq (ISI), turning it into the independent IS group, expanding into Syria in 2013 and then launching its sweeping offensive in Iraq in 2014.
Baghdadi grew up in a family divided between a religious clan and another of officers loyal to Saddam Hussein's secular Baath party.
Years later, his masterstroke as a jihadist leader was arguably to incorporate the ex-Baathists his predecessors had either fought or ignored into his organisation.
It gave his leadership the military legitimacy he personally lacked and formed a solid backbone for the future IS group, whose extremist religious propaganda was combined with formidable guerrilla efficiency.
Uncharismatic and an average orator, Baghdadi was described by his repudiated ex-wife Saja al-Dulaimi, who now lives in Lebanon, as a "normal family man" who was good with children.
Baghdadi is thought to have had three wives, Asma al-Kubaysi, Isra al-Qaysi -- from Iraq and Syria -- and another, more recent, from the Gulf.
He has also been accused of having repeatedly raped girls and women he kept as sex slaves, including a pre-teen Yazidi girl and the US aid worker Kayla Mueller who was subsequently killed.