Leader of Islamic State in Iraq and the Levant has $10m bounty on his head and is said to wear mask when with commanders

Of all the prominent jihadi leaders, Abu Bakr al-Baghdadi, head of the Islamic State in Iraq and the Levant (Isis), is among the most mysterious. And his mystique – for now at least – has only been burnished by his group's capture of the city of Mosul.

Described by some as "the new Osama bin Laden", he has a $10m US bounty on his head, only two pictures of him are known to exist and, contrary to his nom de guerre, he was born not in Baghdad but 78 miles north, in the city of Samarra.

Ambitious and violent, his reputation as a militant leader and tactician is as much a reflection of the disarray of other rebel groups in Syria and the poor showing of the Iraqi army this week.

Baghdadi is said to keep a low profile even among his own armed supporters, who amount to an estimated 7,000 fighters. He is not one for video-taped pronouncements; some reports claim – perhaps fancifully – that he wears a mask when addressing his commanders, earning him the nickname "the invisible sheikh".

What is known about Baghdadi – whose aliases, according to US intelligence, include Abu Dua and Dr Ibrahim Awwad Ibrahim Ali al-Badri al-Samarrai – comes largely from jihadi websites describing his career and accomplishments or his own statements.

Born in 1971 into a religious family, Baghdadi earned a doctorate in education from the University of Baghdad.

There are competing versions of how he came to jihad. One suggests he was a militant jihadist during the time of Saddam Hussein. Others have pointed to the four years he was held at Camp Bucca as the root of his radicalisation.

Another variation describes how, after the US invasion in 2003, he was quickly drawn into the emerging al-Qaida in Iraq under Abu Musab al-Zarqawi, getting involved first in smuggling foreign fighters into Iraq, then later as the "emir" of Rawa, a town near the Syrian border.

There, presiding over his own sharia court, he gained a reputation for brutality, publicly executing those suspected of aiding the US-led coalition forces – the same brutality that has become familiar to those living in Syria under his group's control.

Baghdadi preached and taught at various mosques and apparently led several smaller militant groups before being promoted to a seat on the Majlis al-Shura (consultation council) of the mujahideen and judicial councils of the Islamic State in Iraq, who promoted Baghdadi to succeed the previous two leaders, Abu Omar al-Baghdadi and Abu Hamza al-Muhajir.

Perhaps learning from the lesson of one of his notorious predecessors in Iraq the Jordanian leader of al-Qaida in Iraq, Abu Musab al-Zarqawi – who was reprimanded in a letter by Al-Qaida Central for the excesses of his vioelnce – Baghdadi's prominent supporters have tried to emphasise a leader open to discussions with tribal leaders.

None of this is entirely consistent with his rise to power in the leadership of al-Qaida in Iraq in 2010 – and later of Isis – during which he murdered prominent Sunnis as well as Shia civilians in bombings.

Indeed, part of the problem is that Baghdadi's character – as presented through the writings of jihadi scholars who support him – has been designed to make him more palatable and deliberately cast him, as some analysts have suggested, in the role of a "philosopher jihadi" perhaps to boost his credentials for leadership within the wider jihadi world.

One measure of the success of that tactic is how Isis, under Baghdadi, has become the go-to group for thousands of would-be foreign jihadi fighters who have flocked to his banner. Then, lLate last year a unilateral announcement was made that he was creating a new group that would be merged with a rival al-Qaida affiliate active in Syria, Jabhat al-Nusra. It was a pronouncement disputed both by Jabhat, and Al-Qaida Central's leader, Ayman al-Zawahiri, who ruled against Baghdadi.

Six months ago that was regarded as a moment of serious hubris. Today analysts are wondering whether, after the success of Isis in winning swathes of Iraq, Baghdadi has eclipsed Zawahriri at Al-Qaida Central. Whether that trajectory can continue will depend on the coming weeks and months.

The recent careers of jihadi field commanders have tended to be short after their rise to prominence and notoriety.

And, despite being from Iraq, Baghdadi and his followers will have to negotiate the same complex minefield of competing Sunni interests – including his current allies in Ba'athist insurgent groups, who are ideologically very different. These frictions have led to the downfall of a previous al-Qaida incarnation in Iraq.

That has already been prefigured in Syria where, this year, during his last big play to merge with Jabhat al-Nusra, other rebel groups complained that Isis and Baghdadi were more interested in consolidating its rule over captured towns as part of Baghdadi's plan to establish his own rule than fighting Assad.

There is at least no mystery about what Baghdadi wants. He believes that the world's Muslims should live under one Islamic state ruled by sharia law, the first step of which is establishing a caliphate spanning Syria and Iraq.