Zarqawi was released in Jordan under a general amnesty

The Jordanian-born militant first appeared in Iraq as the leader of the Tawhid and Jihad insurgent group, merging it in late 2004 with Osama Bin Laden's al-Qaeda network.

But most information on him was restricted to what his enemies and supporters have attributed to him.

While many analysts argued he had used the Iraqi insurgency as a springboard to expand his operations, sceptics said his influence was exaggerated.

ABU MUSAB AL-ZARQAWI US $25m bounty on head Linked to Iraqi bombings, assassinations and beheadings Merged Iraqi insurgent group with Bin Laden's al-Qaeda network in 2004 Emerged in Iraq as Tawhid and Jihad group chief Linked to Casablanca and Istanbul blasts, in 2003 Foreign fighter against Soviet forces in Afghanistan in 1980s Jordan petty criminal in youth

In the style of Bin Laden, Zarqawi apparently released a number of audiotapes rallying support and challenge the US and its allies - but he only appeared in one video message, less than two months before his death.

However, videotapes did appear in the name of Tawhid and Jihad - horrific footage showing the beheading of foreign hostages, with Zarqawi himself said to be the man wielding the knife.

In the run-up to the Iraq war in February 2003, US Secretary of State Colin Powell told the United Nations that Zarqawi was an associate of Osama Bin Laden who had sought refuge in Iraq.

Intelligence reports indicated he was in Baghdad and - according to Mr Powell - this was a sure sign that Saddam Hussein was courting al-Qaeda, which, in turn, justified an attack on Iraq.

But some analysts at the time contested the claim, pointing to Zarqawi's historical rivalry with Bin Laden.

ZARQAWI-CLAIMED ATTACKS 28 Oct 2002: US diplomat Laurence Foley killed in Jordan 19 Aug 2003: Bombing of UN office in Baghdad, 23 dead 29 Aug 2003: Bombing of Najaf shrine killing Shia cleric Muhammad Baqr Hakim, 85 dead 2 March 2004: Co-ordinated attack on Shia mosques during Ashoura ceremony, 181 dead 11 May 2004: Nick Berg beheaded, first of at least nine foreign hostages killed in 2004 14 Sept 2004: Car bomb targeting police recruits in Baghdad, 47 dead 19 Dec 2004: Car bombs in Najaf and Karbala, 60 dead 19 Aug 2005: Rocket attack in Jordan on Israel and US navy 9 Nov 2005: Triple attack on hotels in Amman, 60 dead Zarqawi in his own words

They had both risen to prominence as "Afghan Arabs" - leading foreign fighters in the US-backed struggle against Soviet forces in Afghanistan in the 1980s.

It was a far cry from Zarqawi's youth as a petty criminal in Jordan, remembered by those who knew him by his real name - Ahmad Fadil al-Khalayleh - as a simple, quick-tempered and barely literate gangster.

But after the defeat of the Soviets, Zarqawi went back to Jordan in 1992 with a radical Islamist agenda.

He spent seven years in prison there, accused of conspiring to overthrow the monarchy and establish an Islamic caliphate.

Not long after his release under a general amnesty in 1999, he fled the country.

Jordan tried him in absentia and sentenced him to death for allegedly plotting attacks on American and Israeli tourists.

'Zarqawi' shows face in video

Western intelligence indicated Zarqawi had sought refuge in Europe.

German security forces later uncovered a militant cell which claimed Zarqawi was its leader.

Cell members told their German interrogators their group was "especially for Jordanians who did not want to join al-Qaeda".

According to the German intelligence report, this "conflicts with... information" from America.

Kurdish connection

The next stop on his itinerary was said to be his old stamping ground - Afghanistan.

A 'wanted' poster for Zarqawi who had a $25m bounty on his head

He is believed to have set up a training camp in the western city of Herat, near the border with Iran.

Students at his camp supposedly became experts in the manufacture and use of poison gases.

It is during this period that Zarqawi is thought to have renewed his acquaintance with al-Qaeda.

Following the 11 September 2001 attacks and the US invasion of Afghanistan, he is believed to have fled to Iraq after a US missile strike on his Afghan base.

US officials say that it was at al-Qaeda's behest that he moved to Iraq and established links with Ansar al-Islam - a group of Kurdish Islamists from the north of the country.

Sectarian strategy

In October 2002, Zarqawi was blamed for the assassination of US aid official Laurence Foley in Amman.

But it has been in Iraq, though, that he was said to have been most active.

He was blamed for some of the first big insurgency attacks to shake Iraq following the US-invasion to overthrow Saddam.

These included the truck bombing that killed 23 people including UN envoy Sergio Vieira de Mello at the world body's headquarters in Baghdad on 19 August 2003 and the blast in Najaf 10 days later that killed a senior Shia cleric and more than 85 others.

A letter released by the Americans in February 2004 seemed to support their claim that targeting Shias is central to Zarqawi's strategy in Iraq.

In it, Zarqawi appeared to share his plans for igniting sectarian conflict in Iraq as a means of undermining the US presence there.

Within days of the letter's release, bomb attacks on recruiting centres for the Iraqi security forces had killed nearly 100 people.

Another approach that sent shockwaves around the world was the beheadings of foreign hostages, which were posted on the internet in video footage attributed to the Tawhid and Jihad group.

In some of them, Al-Zarqawi himself was said to be the man wielding the knife.

Bin Laden rival?

The US military claimed to have injured Zarqawi in an assault in 2005. A statement released by al-Qaeda appeared to confirm this but said the injuries were minor.

Several men alleged to be key aides of Zarqawi have also been killed or captured - but these appeared to have had no effect on his group's ability to operate.

The US offered a $25m bounty on Zarqawi's head - the same sum they offered for Bin Laden himself.

But in the last year, he seemed to have been able to move his campaign beyond Iraq's borders again, claiming responsibility for a triple suicide bombing in the Jordanian capital Amman in November 2005, as well as other attacks.

Shortly afterwards, the al-Qaeda in Iraq group posted a web statement saying that it had joined five other insurgent groups in Iraq to form a new umbrella group, the Mujahideen Shura Council.

It was also reported that Zarqawi was forced to step down as leader of his group.

A leading Islamist who was behind the reports, Huthaifa Azzam, said some followers had been unhappy about Zarqawi's tactics and tendency to speak for the insurgency as a whole.

But like so much else about Zarqawi's life, the true facts seem likely to remain shrouded in uncertainty.