Abu Musab al-Zarqawi rivalled Osama bin Laden as one of the world's most feared terrorists.
As head of the al Qaida terror network in Iraq, he claimed responsibility for numerous suicide attacks and the beheadings of at least ten foreign hostages, including British engineer Ken Bigley.
There were reports that al Zarqawi (pictured) personally carried out the beheading of 62-year-old Mr Bigley.
The US issued a #13.6 million bounty on the terrorist's head - the same as bin Laden.
Al-Zarqawi was once linked by former US Secretary of State Colin Powell to the ricin plot in London and the murder of Special Branch detective Stephen Oake.
On the eve of the US and British invasion of Iraq in 2003, Mr Powell told the United Nations that alZarqawi and his network had plotted attacks in European countries including Britain.
He said that, according to a detainee called Abuwatia who graduated from al-Zarqawi's Afghan terrorist camp, alZarqawi had sent at least nine North African extremists to Europe to conduct poison and explosive attacks.
Al-Zarqawi, a Jordanian-born Sunni, first appeared in Iraq as the head of militant group Tawhid and Jihad which eventually joined with al Qaida.
He spent time in Afghanistan in the 1980s, leading foreign fighters against Soviet forces before returning to Jordan, where he spent several years in prison over allegations of trying to overthrow the monarchy.
After serving his time, it is thought he sought refuge in Europe before returning to Afghanistan again, setting up a terrorist camp and building up links with al Qaida.
In 2004, al-Zarqawi pledged his allegiance to bin Laden and led an onslaught of attacks against coalition troops.
The militant leader was known for sending taunting
messages, encouraging insurgents to rise up and attack.
His most recent address came in April when he released a defiant video promising more attacks on the West.
Showing his face for the first time on television, he dismissed the new Iraqi government as an American "stooge" and a "poisoned dagger" in the heart of the Muslim world.
Addressing Sunnis in Iraq and across the Arab world, he warned that their community was in danger of being caught between "the Crusaders and the evil Rejectionists" - terms used by radical Sunnis for the
Americans and Iraq's majority Shiites. Al-Zarqawi's shadowy power and influence caused a plethora of rumours about his activities.
In August 2005, he was said to have been overseeing preparations by highly-trained operatives for a "large scale" terrorist attack in Europe, according to intelligence reports.
It was suggested that he had spoken of sleeper cells in Turkey and Iran which may be in contact with European jihadist groups that previously had no links to the terror organisation.
In April 2005, it was claimed that al-Zarqawi had
obtained a nuclear weapon or dirty bomb and was preparing for an attack.
But it was al-Zarqawi's campaign of terror, through bombings and kidnap, that caused most fear.
Outside of Iraq, he claimed to have masterminded a triple suicide bombing against hotels in the Jordanian capital Amman in November 2005 that killed 60 people, as well as other attacks in Jordan and a rocket attack from Lebanon into northern Israel.
He had long eluded all efforts to track him down although US forces are believed to have come close to capturing him several times.