The 44-year-old has been described by a Spanish judge as "Osama Bin Laden's right-hand man in Europe".
And although the British authorities have been more circumspect, they have labelled the Jordanian a "truly dangerous individual".
Qatada is now facing imminent deportation from Britain, 11 years, 10 months and 26 days after he arrived on a forged United Arab Emirates passport to claim asylum for himself and his family.
He has been convicted in his absence in Jordan of involvement with terror attacks in 1998, and of plotting to plant bombs at the millennium.
The radical cleric once called on British Muslims to martyr themselves in a holy war on oppression.
He had links with shoebomber Richard Reid and Zacarias Moussaoui, the "20th hijacker" in the September 11 atrocities.
Tapes of his sermons were found in a Hamburg flat used by some of the September 11 hijackers.
When new laws were passed in December 2001 allowing terror suspects to be detained without charge or trial, Qatada went on the run.
He became one of Britain's most wanted men.
Over 6ft tall and weighing more than 20 stone, he was an unlikely fugitive from his home in Acton, west London, but he avoided capture for 10 months.
Qatada, whose real name is Omar Mahmoud Mohammed Othman, was finally arrested in an armed raid on a council house in south London in October 2002 and held in Belmarsh prison in south east London.
Mr Justice Collins, chairman of the Special Immigration Appeal Tribunal (Siac) which heard an appeal against his detention, said in March last year: "The appellant was heavily involved, indeed was at the centre in the United Kingdom of terrorist activities associated with al-Qa'ida.
"He is a truly dangerous individual."
He added: "We have no doubt that his beliefs are extreme and are indeed a perversion of Islam for the purposes of encouraging violence against non-Muslims and Muslims who are or have been supportive of Americans in particular."
Qatada issued a "fatwa" in 1995 which appeared to justify killing the wives and children of "apostates" to stop oppression of Muslims in Algeria, Siac said.
In 1999, he reportedly made a speech advocating the killing of Jews, that Americans should be attacked and that there was no difference between English, Jews and Americans.
He had "very active involvement" with many groups and individuals linked with al-Qa'ida, the Siac panel said.
In February 2001, the cleric was arrested and questioned by anti-terror officers because he was suspected of involvement with a cell in Frankfurt which plotted to bomb the Strasbourg Christmas market. No charges were brought due to insufficient evidence.
A report by Siac noted: "UK and foreign currency to a value in excess of £170,000 was found in his possession. £805 was in an envelope which recorded that it was 'for the mujahedin in Chechnya'."
Qatada was eventually freed from Belmarsh on conditional bail by Siac in March this year and shortly afterwards was handed a control order designed to limit his movements and contact with other people.
The cleric was labelled "European spiritual leader" of an al-Qa'ida-related terror group by Spanish judge Baltasar Garzon during an investigation into Spanish ties to the September 11 attacks on New York and Washington.
Judge Garzon reportedly claimed that money raised in Spain was sent to Qatada so he could send it on to Mohamed al-Maqdasi, a Jordanian who has been imprisoned for his alleged role in planning a series of bombing attacks in his own country.
Qatada has always denied claims that he is al-Qa'ida's European ambassador, and insisted he has never met Osama bin Laden.
Police in the US, Belgium, France, Germany and Italy have reportedly probed his alleged role as a key figure in the global radical Islamist movement, and several European countries are believed to be trying to extradite him.
Qatada arrived in Britain on September 16, 1993. He was recognised as a refugee in June 1994 and granted leave to remain in Britain until June 1998.
He applied for indefinite leave to remain in May 1998 but his application had not been decided at the time of his original detention.Reuse content