In the recondite world of fundamentalist Islam in Sydney, firebrand sheikhs come and go like the weather, which is to say that they are often loud and sometimes unpleasant but mostly harmless. No sooner has one called for the restoration of the caliphate than another has denounced peep-toe shoes or declared a fatwa on the phrase "Happy Christmas".

Feiz's career, however, has endured longer than most, owing in part to his considerable appeal among youth and his formidable charisma. "You will love to talk to him," one man assured me, "because when you talk to him you will feel like a million-dollar man."

His most inflammatory sermons - those urging children to die for jihad and calling Jews "pigs" - appear to be behind him. Yet Feiz still has a habit of popping up, as when he was linked in April to Boston bomber Tamerlan Tsarnaev, who had posted two of the sheikh's video sermons on his YouTube page. In 2010, he called for the beheading of anti-Islamic Dutch politician Geert Wilders ("This Satan, this devil, this politician in Holland"). In 2011, he was asked by authorities to remove from his website footage featuring the al-Qaeda spiritual leader Anwar al-Awlaki. And in September 2012, some of his supporters were among those who rioted in Hyde Park against the anti-Islamic film Innocence of Muslims. (Feiz denounced the violence and said he told his followers not to go.) He has hosted dinners for the Ayub twins (the founders of Jemaah Islamiah in Australia), shared his home with one-time al-Qaeda confidant Rabiah Hutchinson, and tutored "Jihad" Jack Roche, Australia's first convicted terrorist.

Some time in the past six months, however, something strange happened. Feiz changed. In April, federal Attorney-General Mark Dreyfuss publicly praised him for assisting authorities, noting that his most controversial videos were "some years old", and that, in the wake of last September's riot, the sheikh had co-operated with the federal government's Countering Violent Extremism program.

Police also told me how, after the Boston bombings, Feiz had called them to condemn the violence and make it clear he had no prior knowledge of the plot. The sheikh, it seems, had grown, mellowed. "Life teaches you lots of things," he said in an interview with Muslim Village website. "I am wiser than I was in the past."

Intrigued by this, I started asking around, which is when I discovered that there is no such thing as Sheikh Feiz, only other people's opinions of Sheikh Feiz. Many people tell me that Feiz is "a fantastic guy" and "very generous", that he's a father, with his wife Jacqui, to six children and several foster children.

"He took a lot of young people from drugs and the street," says Moussaab Legha of the Islamic Welfare Centre in Lakemba, in Sydney's south-west. "Multimillion-dollar projects from the police and government, they didn't achieve what he is achieving." One supporter tells me of his love of farming and of animals, especially horses, and how he takes kids to Yathrib Ranch, his property at Kemps Creek in far western Sydney, for pyjama parties and boys' retreats.

Others are less flattering. Feiz's new-found moderation is "camouflage", apparently. Some accuse him of "brainwashing" local boys, of filling their heads with his hardline Salafi ideology. Most of the people I speak to - even the sheikh's supporters - aren't prepared to be named. "If I talk, I am scared for my safety," one man explains. "You should be, too."

The result, when it comes to Feiz, is a virtually impenetrable wall of silence and self-censorship. One day, after much cajoling and low-level begging, I manage to secure an interview with a prominent and well-connected Muslim community leader in south-west Sydney. The man, who I'll call Rafik, is tall and urbane, dressed in a white skivvy and pressed trousers. His secretary, a woman in a headscarf, serves us hot sweet coffee in tiny tumblers.

"Feiz's ideas are harmful to our society," Rafik tells me. "He is not building institutions, he is building followers for himself."

I explain how almost everybody I have contacted has refused to talk with me, on the record at least. "People are afraid," Rafik says. "But he is a leader. He shapes people's views, so he has a responsibility to talk with you. You have to ask, 'What is he trying to hide?' "

Then, without warning, Rafik rises and walks to the door. I follow him, a little confused. Before ushering me out, Rafik pauses. "Just one thing," he says, bathing me in his sweetest, warmest, broadest smile. "Don't ever call me again. It's nothing personal, I just can't be talking to you about this any more."

According to the prophet Muhammad, "charity" is a good word. Sadly, Sheikh Feiz did not have any words for me, good or otherwise. For a solid month I tried to contact him, via telephone, email, texts, Facebook - I even wrote him a letter - but he resolutely ignored me. I would drop in at Bukhari House, the Islamic bookstore and prayer hall in Auburn, western Sydney, where he is the imam, in the hope of catching him. Eventually I got a call from a man who identified himself as the sheikh's "spokesman". "The sheikh will not be doing an interview," he said, so I should stop "harassing" him. "He is just a religious man who does not want to get involved with these things."

The sheikh's silence is regrettable, since by all accounts he has a remarkable story. Born in 1970 in St George, in southern Sydney, he grew up in a large, nominally Muslim family, to parents who had immigrated from Tripoli, in northern Lebanon. "At school he was just a normal Aussie kid," says Muslim Village editor Ahmed Kilani, who was in Feiz's year at Hurstville Boys High School. "He played cricket in the playground and all that. But I recall he wasn't that religious, because he'd hardly ever come and pray with the rest of the Muslim boys at lunchtime and on Fridays."

Feiz left school after year 10 to learn carpentry and carpet-laying. He also started hanging out on the streets, doing drugs, drinking, and getting into fights. "I got a bit nasty," he told journalist Cameron Stewart in 2003. "A lot of drugs, a lot of evil stuff." He took up boxing, partly to defend himself, training at the St George PCYC, where he met future Australian amateur champion Mick Akkawy. "He fought a couple of times at the PCYC," says Akkawy, who was friends with Feiz's older brother, Fawaz. "He'd also started bodybuilding, so he had a good physique."

Combat was a natural fit for Feiz, the ideal outlet for his restive ambition and wounded temperament. Adopting the ring name "Frank the Killer", he ascended the ranks and was, by 1987, the NSW amateur welterweight champion. He then turned to bodybuilding ("Frank the Killer" became "Frank the Beast") and, in 1989, won the national under-19 bodybuilding title. Yet his extra-curricular activities were taking a toll. "I actually feared death or imprisonment, because that was the next step in my life," he later admitted.

And so, at 19, he turned to religion, embarking on an exploration first of Christianity, then Buddhism and, most improbably, Judaism. (He reportedly attended a synagogue in Sydney's eastern suburbs but came to feel that Arabs weren't welcome.) Then came Islam, and with it, said Feiz, "the truth". But the Islam of his rebirth would not be that of his upbringing; instead of the in-name-only beliefs of his parents, Feiz pursued a purer, ultra-pious Islam, courtesy of the radical Melbourne-based Sheikh Mohammed Omran, of whom Feiz became a devoted student.

Then as now, Sheikh Omran was the emir of the Ahlus Sunnah Wal Jamaah Association of Australia (ASWJ). Established in 1989, ASWJ espouses an ultraconservative form of Islam known as Salafism, the teachings of which adhere to the practice of the first three generations of the Muslim community, beginning with the Prophet and his companions. Salafism is Islam stripped bare; puritanical, literalist and often irresistible to those, like Feiz, who crave clarity and guidance. As he explained: "I don't believe in unclear concepts. Everything divine must be clear."

Feiz flourished under Sheikh Omran, who sent him, in 1990, to Saudi Arabia's Islamic University of Madinah, where he studied two years of Arabic and four years of Islamic law. He returned in 1997 as Sheikh Feiz and promptly established a musallah, or prayer centre, in Haldon Street, Lakemba. His sermons were an almost instant success. "Sheikh Feiz is a sheikh for the youth," says former terror suspect Zaky Mallah, who was one of his first students. "He was a boxer, too, so he understood the mentality of his generation, and because of that a lot of people related to him and he related to them."

Feiz's following grew rapidly thanks to the fact he spoke English - a huge advantage in an area then dominated by Arabic-speaking imams, whose sermons were largely lost on the youth. But equally important was his ability as a communicator. In short, Feiz is a dynamite performer. His talks, which you can see on the web, are an oratorical roller-coaster ride, jam-packed with pregnant pauses, repetition and radical gear shifts - serene to severe in a nanosecond - not to mention the hysterical hand gestures, elaborate syntax and, perhaps his signature device, the lingering, sibilant "s" ("sinnerssss" ... "tribulationsssss").

Coupled with his glowering features - the beard, the brow, the thunderbolt eyes - Feiz's talks are rarely less than mesmerising, scouring admonitions on the perils of everything from illicit intercourse to the USA, or "the United Snakes of America", as he prefers to call it.

By 2000, Feiz had set up another western Sydney musallah, the Global Islamic Youth Centre in Liverpool, which regularly hosted hundreds of his supporters, including former rugby league star Hazem El Masri and boxer Anthony Mundine. Mundine would often visit Feiz's farm and ride his horses. El Masri, whom Feiz had met in Saudi Arabia while the footballer was on pilgrimage, was a particularly vocal supporter. "[The sheikh] is a good guy, and is trying to guide a lot of the young guys along the right path," he said. (Neither Mundine nor El Masri would comment for this story.)

Yet Feiz's sermons were, more often than not, pure invective. He would warn his flock to avoid the dreaded kuffar, or non-Muslims ("They are evil, they are cunning, they desire to harm you severely"), as well as "filthy, disgusting" Jews. (One lecture told the story of the Jewish man who seduces and impregnates a Muslim virgin, only to then kill her and the baby.) His message was simple: Islam = good, homosexuals = cursed, women = rape magnets, jihad = great. "We want to have children and offer them as soldiers defending Islam," he says in one video lecture. "Teach them this: there is nothing more beloved to me than wanting to die as a mujahid."

For some in the audience, such talk proved intoxicating. "At long last we've got someone who has something to say about Islam," Jack Roche reportedly told a neighbour after hearing Feiz speak. "You get sick of ... listening to all the bullshit." (Arrested in 2002, Roche was sentenced to nine years in prison in 2004 for plotting to blow up the Israeli Embassy in Canberra, the planning of which had been undertaken using a video camera borrowed from Feiz. He was released in 2007.)

By 2005, Feiz's following was estimated at 4000 people - mostly impressionable, dispossessed, angry young men. "I was friends with these guys," one young Muslim told me. "I grew up with them in Lakemba. They all came from a gangster background. And that was what attracted them to Feiz in the first place. They thought, 'Cool, I get to keep my ways and I go to heaven.' "

But Feiz's influence was not going unnoticed. "Sheikhs like Feiz ruin people," said Mamdouh Elomar, father of Feiz protégé and champion boxer Ahmed Elomar. "I know my religion, so I can tell him when he is wrong, but these kids believe everything he says."

In 2006, defying his father's wishes, the 24-year-old Elomar followed Feiz to Lebanon, where the sheikh had gone to care for his ailing father. Accompanying him were Ibrahim Sabouh, a financial adviser who was said to have managed the Global Islamic Youth Centre accounts; Mohammed Basal; and a Sydney cabbie named Omar Hadba. All four were arrested in Tripoli a year later, when police uncovered a large cache of Kalashnikovs, rocket-propelled grenades and landmines in Hadba's garage. According to Lebanese police, the weapons were intended for Fatah al-Islam, a Salafi group fighting to replace the Lebanese government with an Islamic regime. (Basal and Elomar were released, but Hadba and Sabouh were convicted in 2011.)

Lebanese authorities also wanted to interview Feiz, but the sheikh had already left, this time for Malaysia. "I know they want to talk to me but I am not afraid because I haven't done anything," he told Sydney newspaper The Sun-Herald. "I will leave it in God's hands."

Boxing teaches you lots of things: how to attack, obviously, but also, perhaps more crucially, how to duck and weave. Feiz understands this. Despite what one Islamic leader calls his "big mouth", the sheikh has remained adept at double moves, a master of the slip and feint. As early as 2003, for example, at the same time he was comparing the West to a stinking toilet, Feiz was regularly updating ASIO on his own congregation. ASIO would return the favour, protecting him from what the sheikh alleged was police harassment. "I called ASIO and they stopped it," he said at the time. "I haven't had one problem since."

In 2007, however, while still overseas, Feiz again ran into trouble, this time thanks to his Death Series, DVD lectures in which, among other things, he called for the killing of kuffar. The series was a big hit; copies turned up for sale outside mosques in London. Back in Australia they were labelled "an incitement to terrorism"; Australian federal police even raided the Global Islamic Youth Centre. For a while, the sheikh seemed close to being charged with sedition. "I would say this to Sheikh Mohammed," then federal opposition leader Kevin Rudd said. "Do not return to Australia, you are not welcome."

Yet by 2010, Feiz was back. For a time he stayed quiet. He gave talks, he farmed, he raised funds for charity (often this meant giving cash to the families of imprisoned Muslims). He also performed marriage counselling. "He was fantastic," the Islamic Welfare Centre's Moussaab Legha tells me. "He explains [to the wife] how important it is to co-operate with her husband: you are divorcing him, yes, but he is still the father and you will have reward and blessings, and so he explains what the rewards will be in the hereafter."

Before long, however, suffering perhaps from controversy cravings, Feiz had launched a veritable fatwa frenzy, issuing rulings on everything from Harry Potter ("promotes paganism") to rugby league ("the devil's game") and mixed-sex education. "If a Muslim wife, sister or daughter sits in a classroom with a male professor and other men around her, it's as if she were cheating on you," he said. Some of his rulings were highly problematic, such as when he declared mortgages haram, or forbidden, since they involved paying interest, a concept prohibited under Islam. (In the end, some Muslims, desperate to buy their first homes, secretly sought individual fatwas from more experienced sheikhs, giving them permission to take out loans.)

"The mistake was when he started taking stances that were much bigger than his qualifications," says prominent Australian Muslim leader Sheikh Taj el-Din al Hilaly, who was soon fielding calls from fretful parents. "They were afraid, because their kids had changed. [Feiz] was programming them. Now they felt like only they had the truth. They'd tell their mum, 'You are wrong!' Or, 'Dad, you are wrong!' Elections were haram, parties were haram, music was haram, cinema, TV, buying your house - everything was haram."

At the same time, Feiz's "boys" began earning a reputation as Islamic enforcers; in one instance they broke into a Muslim man's home in Silverwater and flogged him 40 times with a piece of electrical cord for drinking beer. Using Bukhari House, the Auburn bookstore and prayer hall, as a base, they would harass and intimidate local shopkeepers, particularly Shias, whom Salafis consider heretics. "They stand out the front of my shop and tell people walking past, 'Don't come in here, only shit people work here,' " said one Iraqi Shia. Jamal Daoud, a local politician and outspoken Shia, believes Feiz's ultimate goal is to push moderate Muslims out of the area and buy up their properties on the cheap.

Before long, anxious parents were sending their kids overseas, back to Turkey in many instances, to steer them away from Salafi influences. But it was the 2011 NSW state election that really brought matters to a head, when men from Bukhari House repeatedly tore down election posters from the local shops (Salafis consider voting to be haram).

Jamal Daoud, whose posters were repeatedly targeted, followed one of the men, Milad Bin Ahmad Shah al-Ahmadzai, back to Bukhari House and confronted him. "I said, 'Why are you taking my posters down?' " Daoud tells me. "And Milad said, 'Because democracy is not allowed in Islam. You are Muslim, and you're not supposed to take part in this election.' He became furious with me and so I left."

Feiz has since acknowledged that voting is a part of life in Australia. But his wife, for one, doesn't seem convinced. Her Facebook page features a photo of bullets all lined up in a row, with the tagline: "Voting: like being able to choose which bullet you'd prefer to be shot in the head with."

There are many words Sheikh Feiz Mohammed can't abide, but chief among them is the phrase "non-Muslim". "I prefer to say not-yet-Muslim instead of non-Muslim," he told Muslim Voice in 2012. "It's a bit more, sort of, sweeter."

Like all fundamentalists, the sheikh is not given to notions like nuance or compromise. The world is essentially, unavoidably Manichean - a never-ending spiritual battle, a zero-sum struggle where enemies abound. The subsequent clannishness of his followers, their almost fanatical secrecy and defensiveness, is one of the hallmarks of Salafism, which is now thought to be the fastest-growing Muslim movement in the world.

In Australia, the great majority of Muslims are mainstream moderates, and just 10 per cent are Salafis. But the Salafis' rapid spread, not to mention their unblinking fervour, makes them something to behold.

One morning, for instance, while visiting Bukhari House, I get talking to a young man behind the counter. He is wearing a black robe and the signature Salafi beard. He asks me if I have read the Koran. I say I have not.

He says he is currently in the process of memorising it. "Do you know that in the 1433 years since it was written, not one scientist has been able to disprove it?"

"Really?" I say. "Really!" he says. "The Koran explains perfectly how embryos are formed, how the stars were made. That's why scientists have taken all their stuff from the Koran."

Life isn't easy as a Muslim, though. The beard makes it hard to get a job. But it doesn't matter, since he is "put here on earth for one reason - to worship Allah. And if we don't worship him, he has the right to put us in hellfire."

for feiz, guys like this are a mixed blessing. They are loyal, yes, but their loyalty demands a constant diet of hardline rhetoric. "Feiz has become hostage to his followers," Muslim Village editor Ahmed Kilani tells me. "As some sheikhs grow older and wiser, they, like everyone else, can sometimes change their previous ideas. This change is often too hard to accept for some of their followers and I sense this may have happened with Sheikh Feiz. He seems to have mellowed out over the years, but the price of this is rejection by some of his followers who have moved on to other sheikhs more in keeping with their hard-hearted approach."

According to Kilani, Feiz lost credibility with some of his followers after the Sydney protest riot. "Some hardliners felt insulted when he criticised the rioters last year." Others were affronted when he suggested, in 2011, that he might be able to work with Sufis, a mystic Islamic group Salafis traditionally detest. In the notoriously fractious ecosystem that is Islam in Sydney, Feiz's former followers would have no shortage of alternative sheikhs to choose from, including the increasingly voluble clerics at al-Risalah, an Islamic bookstore in Bankstown.

Perhaps Feiz isn't bothered by this. Perhaps he is. Perhaps, as one Muslim community leader suggests, he is simply plotting his next move, into a more political role.

In the meantime, all remains gloriously, typically, mysteriously opaque. "I am extremely comfortable with the way things have worked out, and are working," Feiz told Muslim Village in an interview last year. "So let us forget what has happened, and let us focus on today."

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