British hate preacher Anjem Choudary has been jailed for five years and six months at the Old Bailey for drumming up support for Isis.
His supporters in the public gallery shouted "Allahu Akbar" as Choudary was sentenced. Taking time already served in custody, he could be out by early 2019.
The British-born 49-year-old backed the terrorist group in a series of talks posted on YouTube, and recognised a caliphate - a symbolic Islamic state - had been created under an Isis leader after it was announced In June 2014.
Despite being a leading figure in the banned group al-Muhajiroun (ALM), and with a series of former supporters going on to be convicted of terrorism, Choudary had stayed on the right side of the law for two decades.
But the pledge of allegiance posted online was the breakthrough the police needed.
Choudary and Mohammed Mizanur Rahman, 33, from Whitechapel, east London, who was also jailed for five and a half years, were found guilty of inviting support for Isis (Islamic State) between June 29, 2014 and March 6, 2015.
Jailing the pair, Mr Justice Holroyde said the offences were serious given their influence over impressionable people at a crucial time when Muslims were looking for guidance on the Isis caliphate claims.
He told Choudary: "You did nothing to condemn any aspect of what Isis was doing at the time.
"In that way you indirectly encouraged violent terrorist activity."
He described Rahman as a "hothead" while Choudary was more "calculating" and the more experienced.
Both men were dangerous and had shown no remorse, he said.
"You are both mature men and intelligent men who knew throughout exactly what you were doing. You are both fluent and persuasive speakers."
Sue Hemming, CPS Head of Counter Terrorism said: "Both men were fully aware that Daesh is a proscribed terrorist group responsible for brutal activities and that what they themselves were doing was illegal. Those who invite others to support such organisations will be prosecuted and jailed for their crimes."
In one speech in March 2013, Choudary, from Ilford, north-east London, set out his ambitions for the Muslim faith to "dominate the whole world".
He said: "Next time when your child is at school and the teacher says, 'What do you want when you grow up? What is your ambition?', they should say, 'To dominate the whole world by Islam, including Britain - that is my ambition'."
Supporters included Michael Adebolajo and Michael Adebowale, the murderers of Fusilier Lee Rigby, and suspected Isis executioner Siddhartha Dhar.
Shortly after the announcement of the caliphate, Choudary held a meeting with his closest aides to discuss it.
Before accepting it was legitimate, he also consulted his "spiritual guide", Omar Bakri Mohammed, currently in jail in Lebanon, and Mohammed Fachry, the head of ALM in Indonesia.
Next time when your child is at school and the teacher says, 'What do you want when you grow up? What is your ambition?', they should say, 'To dominate the whole world by Islam, including Britain - that is my ambition'
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On July 7 2014, the trio's names appeared alongside Rahman's on the oath posted on the internet, which stated the Muhajiroun had "affirmed" the legitimacy of the "proclaimed Islamic Caliphate State".
The defendants followed up by posting on YouTube a series of lectures on the caliphate, which Choudary promoted to more than 32,000 Twitter followers.
The married father-of-five denied encouraging his followers to back the terror group and insisted the oath had been made without his knowledge. He said of the pledge: "It is completely unnecessary. For the rest of the Muslims it is obedience from the heart".
Despite protesting his innocence, he continued to express extreme views, refusing to denounce the execution of journalist James Foley by so-called Jihadi John, aka Mohammed Emwazi, in Syria in 2014.
He told the jury: "If you took an objective view, there are circumstances where someone could be punished".