Radical cleric Abu Qatada, who gave up his battle against deportation from the UK, has been described as a "truly dangerous individual" and a "key UK figure" in al-Qaeda-related terror activity.
The Palestinian-Jordanian, whose real name is Omar Othman, fought for eight years against deportation to Jordan. He was finally flown out of the UK in July 2013, Less than a year later he was acquitted in Amman's State Security Court of conspiracy to carry out terrorist acts in 1998.
His removal from the UK came after years of legal battles all the way to the European Court of Human Rights and back again. His initial defeat at the Special Immigration Appeals Commission (Siac) in February 2007 had represented a major victory for the government's strategy of finding ways to deport terrorism suspects who it said could not be tried in the UK.
Abu Qatada then appealed to the higher courts saying that evidence extracted through torture would be used against him in Jordan, where he faced a retrial in relation to alleged plots.
That legal battle continued until May 2013, when the cleric accepted that his right to a fair trial in Jordan had been protected by a new treaty between the two countries. He agreed to drop his legal challenge, paving the way for his deportation.
The scholar, who is in his fifties, arrived in the UK in September 1993 and claimed asylum on the basis that he had been tortured in Jordan. He had been living in Pakistan near the Afghan border shortly before his arrival in the UK.
In 1994 he was recognised as a refugee and allowed to remain.
He was among a large group of Islamists who sought refuge in the UK during the late 1980s and the 1990s as they fled from despotic Arab regimes that they had been seeking to overthrow.
Abu Qatada became an important player in the London Islamist scene, later dubbed "Londonistan" by its opponents, because of his credentials as a scholar. He had developed militant views that put him firmly in the fold of hardline thinkers who provided the intellectual arguments for religiously-justified violence. Although his political relationship with al-Qaeda was never straight forward, his worldview became virtually indistinguishable.
During his early years in London, Abu Qatada preached at the Fourth Feathers community centre near Regent's Park and held meetings in his own home, both of which became a hub for exiled Islamists.
Abu Qatada advocated imposing Islamic government on Muslim lands. He said that Islamic law justified taking up arms against despots and foreign invaders because they were the enemies of Muslims.
As the UK's security agencies tried to make sense of the Islamist scene, MI5 approached Abu Qatada on more than one occasion to ask for his help in minimising the threat to the UK.
Security chiefs knew that his influence was broad, particularly among Algerian and Egyptian armed Islamists. His theorising went to incredible lengths in all areas of life. He once debated whether it was Islamically permissible to obey traffic lights in the West.
It was one religious opinion during 1995 which led to devastating consequences. Abu Qatada concluded that it was Islamically lawful to kill the wives and children of "apostates", those who have rejected Islam, to stop oppression in Algeria.
The practical effect was that armed Islamists in the country used his ruling to justify their attacks against civilians on the basis that anyone who was not with them was against them.
The authorities realised his views were hardening against the West, particularly after a sermon targeting Jews. And by 2001, the cleric issued rulings justifying suicide attacks, as seen in a BBC Panorama interview the same year.
A Spanish judge, Baltasar Garzon, described Abu Qatada as the "spiritual head of the mujahideen in Britain", so the question for the UK authorities was whether he now supported "martyrdom operations" against Western targets.
The Security Service and police concluded that Abu Qatada was a threat. In a court statement they said he was providing advice that gave religious legitimacy to those "who wish to further the aims of extreme Islamism and to engage in terrorist attacks, including suicide bombings".
The authorities said that a number of people arrested in connection with terrorism had described Abu Qatada's influence. Richard Reid, the would-be mid-Atlantic shoe bomber, and Zacarias Moussaoui, both jailed for involvement in terrorism, are said to have sought religious advice from him. The cleric's sermons were found in a flat in the German city of Hamburg used by some of those involved in 9/11.
When Abu Qatada was questioned in 2001 over his alleged connections to a German cell, police found £170,000 cash in his home, including £805 in an envelope labelled "For the mujahideen in Chechnya". No charges were brought.
But on the eve of a new law enabling the authorities to hold foreign terrorism suspects without charge or trial, he disappeared. He was later tracked down to a council house in south London and taken to Belmarsh Prison.
The Law Lords eventually ruled such detention illegal and Abu Qatada was among those subjected to a control order, a form of house arrest.
In 2005, he was rearrested and told he would be deported to Jordan, where he had been convicted in his absence of alleged involvement in a plot to target Americans and Israeli tourists during the country's millennium celebrations.
What is not publicly clear is exactly where he now stands. Some influential Islamists have in recent years rejected al-Qaeda, in particular Libya's largest jihadist group.
In December 2005, Abu Qatada made a video appeal to the kidnappers of British peace activist Norman Kember in Iraq. That recording, made inside Full Sutton prison, near York, where he was awaiting deportation proceedings, was broadcast in the Middle East. The question was whether this appeal was genuine, or simply tactical.
In 2008 he was briefly allowed out of prison on bail, while continuing his deportation legal battle. Mohamed Ali, who runs the Islam Channel on satellite television, has known the cleric for years and held talks with him during that period out of jail.
He told the BBC: "Abu Qatada has no links with terrorism [or] al-Qaeda and he never ever agreed or endorsed what was done in 9/11 in America or 7/7 in the UK.
"He said that if he had known that something was going to happen, he would lock them up. He thinks that jihad is limited to either defending Muslim lands when invaders come to Muslim lands or if force is being used to overthrow dictatorship regimes.
"He believes that the covenant between any Muslim coming to this country and the government stands - and it should be honoured by both parties."
But Bob Quick, former head of counter-terrorism at Scotland Yard, does not buy this argument.
He said: "I would describe Abu Qatada as very dangerous, a man with significant influence, significantly well networked in Europe and the Middle East with very extreme views, and prepared to promulgate those views and influence the views of others and their conduct.
"He was very well networked, very well connected, with al-Qaeda. He was an active supporter of terrorism and extreme Islamist objectives through terrorism.
"It might be dangerous at this stage to suggest his influence has waned.
"It may have waned because he's been in custody, mostly, for the last few years but to suggest that he couldn't operate and pick up contacts and reposition himself in the future is probably a bold assumption."
Such views were the reason that successive governments pursued Abu Qatada's deportation so doggedly - and he will never be allowed to set foot in Britain again.