Just over one week ago, US warplanes roared into action over Sinjar Mountain in northern Iraq to support Kurdish Peshmerga fighters as they struggled to fight their way into the area to liberate hundreds of Iraqis being held captive by the Islamic State (Isis).

It was a successful strike and it soon became clear that a handful of senior commanders had been killed. As excitement grew in Washington there were high hopes that the victims would include Isis's much-wanted leader, Abu Bakr Al-Baghdadi, but it was not to be. Among those killed was Abd al Basit, described as the group's military "emir" and Haji Mutazz, a deputy to Baghdadi, but there was no sign of Isis's main man having been killed.

As had happened in the past, reports of his demise turned out to be exaggerated; the "scarlet pimpernel" of the Islamic State was still on the loose. The outcome should come as no surprise to those who have watched the inexorable rise of the movement which aims to create a ­caliphate stretching from the shores of the Mediterranean to the waters of the Gulf.

Slowly but surely it has come into being during the course of the past year and, despite the Nato intervention, it looks unstoppable.

Using coercive methods which seem to belong in the past, Isis fighters have taken on and defeated the Iraqi and Syrian armies - both equipped with modern weapons - and against all the odds they have captured huge swathes of ­northern Iraq and western Syria, the so-called "Fertile Crescent" which includes some of the richest land in the Middle East.

Its fighters have proved to be tough and resilient even in the face of Nato airstrikes but in the greater scheme of things they owe their existence to the shadowy figure of Baghdadi, who has not been seen in public since July.

Not much is known about this man who started life as Ibrahim Awwad Ibrahim Ali al-Badri in his home city of Samarra in the so-called "Sunni Triangle" to the north of Baghdad.

As a child he appeared to be quiet and retiring and, even in the Al-Jibriya district which is renowned for maintaining religious values, he was considered to be especially pious, rarely seen in public without a pile of books under his arm. His aura increased when he let it be known that he was directly descended from the Prophet Muhammad.

Following the US-led invasion of Iraq in 2003, Samarra was singled out for special attention by the coalition forces, being heavily bombed in an attempt to root out dissidents. By then in his ­twenties, al-Baghdadi - as he had become - had moved to study in Baghdad where he gained a doctorate and underwent a process of self-radicalisation by helping to establish the terrorist group Jamaat Jaish Ahl al-Sunnah wal Jamaa. Even though some members of his family had worked for the Saddam Hussein regime, he proved a willing recruit and drifted into the circle of radicals surrounding the Jordanian jihadist Abu Musab al-Zarqawi.

It came as no surprise when he was rounded up by US security forces in either 2004 or 2005 and detained in Camp Bucca, a facility in southern Iraq, near Umm Qasr.

From this distance in time it is difficult to know how much of this background has been created by Isis propaganda - many jihadists from this period were in fact secular Ba'ath Party members - but while Baghdadi's motives might be unclear he was listed as a Sunni "foot soldier" by US intelligence.

What is known is that Camp Bucca became an important training ground and seminary for the young jihadists who were held there.

Certainly, it was from this period that the first steps were taken to form an umbrella fundamentalist group which would reflect the aspirations of the young Muslims caught up in the ­insurgency against US forces. It is also from this moment that dissatisfaction began to mount against al-Qaeda, which had never previously had a presence in Iraq, and the first steps were taken to found the Islamic State in Iraq and al-Sham (the Levant).

From the outset, its aim was to recreate a caliphate in the Middle East which would inspire a younger generation of Muslims. By 2013, al-Baghdadi had emerged as the leader of Isis and was showing a ­precocious determination to turn it into an alternative state, one which would not only take on the Western powers but would also be a focus for Islamic radicalism.

To begin with, the orga nisation's claims were greeted with some disbelief, as if the concept of a caliphate was too grandiose and too ambitious to come into being, but this year's military gains have shown that Isis is a force that demands serious attention.

During the course of the year, too, al-Baghdadi became better known as the leader of Isis and was hailed as its caliph - but that, too, created a conundrum. The more famous he became the less likely it was that he would be seen in public and the more that people spoke about him the less likely they were to have actually met him.

Like many other terrorist leaders before him, al-Baghdadi is constantly on the move, rarely staying in one place for more than one night and if possible never revealing his face to strangers. It is quite likely that he employs a body double and it is equally possible that he plays on his followers' paranoia by turning up to ­meetings unannounced and unheralded.

Even his domestic life is open to ­question. Earlier this month, Lebanese security forces announced that they had arrested his wife and daughter but, while two women were certainly ­apprehended in the Bekaa Valley, Isis sources simply announced that al-Baghdadi had two wives and that one of them might or might not have travelled to Lebanon. The mystery makes him a powerful adversary and the security surrounding his way of life makes it extremely unlikely that he will accidentally fall into the hands of his enemies.