In quotes: Anwar al-Awlaki
US-born Anwar al-Awlaki, who has been killed in Yemen, was originally considered a moderate. But his language hardened over time and he went from condemning terrorism to actively promoting it. At the time of his death he was a suspected al-Qaeda leader.
What Awlaki said
On the 9/11 attacks on the US:
He told the Washington Post in October 2001: "Muslims still see [Osama] Bin Laden as a person with extremely radical ideas. But he has been able to take advantage of the sentiment that is out there regarding US foreign policy.
"We're totally against what the terrorists had done. We want to bring those who had done this to justice. But we're also against the killing of civilians in Afghanistan."
On radical talk:
He told the New York Times the same month: "In the past we were oblivious. We didn't really care much because we never expected things to happen.
"[Since 9/11] things are different. What we might have tolerated in the past, we won't tolerate any more.
"There were some statements [from imams] that were inflammatory, and were considered just talk, but now we realise that talk can be taken seriously and acted upon in a violent radical way."
On the US and the West:
He said in a November 2010 internet post: "Fighting the devil doesn't require consultation or prayers seeking divine guidance. They are the party of the devils.
"Fighting them is what is called for at this time. We have reached a point where it is either us or them.
"We are two opposites that will never come together. What they want can only be accomplished by our elimination. Therefore this is a defining battle."
On Arab leaders:
Also in his November 2010 video message: "Kings, emirs and presidents are not now qualified to lead the nation, or even a flock of sheep.
"If the leaders are corrupt, the scholars have the responsibility to lead the nation."
About Fort Hood shooting suspect Maj Nidal Malik Hasan:
Mr Hasan, accused of shooting dead 13 people at the military base, had seen Awlaki preach in Virginia in 2001 and received religious advice from him by email.
Awlaki told al-Jazeera after the November 2009 attack: "Nidal Hasan is a hero. He is a man of conscience who could not bear living the contradiction of being a Muslim and serving in an army that is fighting against his own people.
"My support to the operation was because the operation brother Nidal carried out was a courageous one."
What others said about Awlaki
Michael Leiter, director of the US National Counterterrorism Center:
"I actually consider al-Qaeda in the Arabian Peninsula, with Awlaki as a leader within that organisation, probably the most significant risk to the US homeland," he said in February 2011.
"[Awlaki] certainly is the most well-known English-speaking ideologue who is speaking directly to folks here in the homeland.
"He probably does have the greatest audience on the internet and the like. So in that sense he is the most important."
US Director of National Intelligence Dennis C Blair:
Though he did not specifically name Awlaki as a target, he was spoke in April 2010 after President Barack Obama's alleged approval of Awlaki's "killing or capture".
"We take direct actions against terrorists in the intelligence community," said Mr Blair.
"If we think that direct action will involve killing an American, we get specific permission to do that."
UK intelligence service MI5 Director General Jonathan Evans:
"The operational involvement of Yemen-based preacher Anwar al-Awlaki with al-Qaeda in the Arabian Peninsula is of particular concern given his wide circle of adherents in the West, including in the UK," he said in a September 2010 speech.
"His influence is all the wider because he preaches and teaches in the English language which makes his message easier to access and understand for Western audiences."
Muddassar Ahmed, London PR company boss:
"At the time he was a very charismatic, knowledgeable, charming preacher," he said, of Awlaki's lectures during visits to London in 1999.
"Years later, when I realised Anwar al-Awlaki was now public enemy number one and the Bin Laden of the internet, I was shocked at his transformation."
Alexander Hitchens, of the International Centre for the study of Radicalisation:
"Awlaki felt safe exploring and expressing extreme views," he said, of Awlaki's time in London during the early 2000s.
"He was promoted by a number of institutions in London at the time and that enabled him to gain a large following of British Muslims - some of whom are still with him to this day."
Rashad Ali, former member of Islamist group Hizb-ul-Tahir and now director of think-tank Centri:
"He was very clear about having this revolutionary jihadist approach. He started delivering lectures on jihad that came out in 2003," he said.
"He gave very explicit verdicts on suicide bombing being religiously acceptable, about the enforcement of religious law and about how jihad in its medieval military form is still necessary today as an imperialist objective."
East London Imam Usama Hasan:
"His approach was all about us versus them, which concerned me. I thought his talk was likely to inflame people's tensions but not tell them what to do. That troubled me."