Until his entry into the global media spotlight as the shadowy figure at the centre of the Sydney siege, Man Haron Monis had long been viewed as a fringe figure in Sydney’s Islamic community, his self-radicalisation rooted in grievances against the Australian government and increasing marginalisation among his peers.

The self-proclaimed spiritual healer had achieved a degree of notoriety as the author of “grossly offensive” letters sent to taunt parents and relatives of Australians killed by extremism in Indonesia as well as troops who lost their lives in Afghanistan between 2007 and 2009.

Well known to the Australian police, he had been consumed by his conviction for the offence, unsuccessfully challenging the conviction in the high court last year and making several vehement and erratic public statements claiming to be innocent.

Monis lost another bid to have the matter heard before the high court on Friday.

He also faced numerous charges relating to his time working as a “spiritual healer” – including 22 counts of aggravated sexual assault and 14 counts of aggravated indecent assault – and had been bailed for allegedly being an accessory to the killing of his former wife.

When Monis, who was also known as Mohammad Hassan Manteghi, appeared in court in October over the sex assault allegations, police charged him with 40 additional offences. It was alleged that he had advised a 27-year-old woman to visit him at his business in Wentworthville in 2002 after she contacted him through a “Spiritual Consultation” ad in a community newspaper.

He was charged last year with being an accessory to the murder of his 30-year-old former wife Noleen Hayson Pal, a mother-of-two who was allegedly stabbed to death and set alight in April 2013.

Iranian-born, Monis sought asylum in Australia in 1996, telling ABC News in 2001 he fled after falling foul of the Iranian regime, which he said had placed his wife and children under house arrest. “I can say they are hostage,” he said at the time, having reportedly given himself the title Sheikh Haron.

As recently as last week on a website he used both to defend and promote himself, he announced that he had converted from Shia to Sunni Islam and pledged his allegiance to the caliphate declared by the militant group Islamic State. That website was shut down as Monday’s siege developed, and police asked media outlets to refrain from giving him a platform as he held 17 hostages in the Lindt cafe in Martin Place.

Sydney Shia leaders had apparently urged federal police to probe his claim to be a leading cleric, while he was ignored by the Sunni community. He had no links to the Islamic State terrorist group, and despite his criminal past was not seen as a likely exponent of the group’s ideology.

One upshot, some would argue, is that he fits bill of a classic lone wolf – a profile that had been much feared by security officials. Monis is believed to have been a self-starter, who had attached himself to the virulent worldview of Isis. His self-radicalisation appeared to be rooted in grievances against the government and fueled by his increasing marginalisation.

Earlier this month, Monis had posted on his website that Shia muslims were rejectionists – a key message of extremist Sunnis in the Middle East.

But there were other hints on the web post that Monis had become radicalised: a rambling October letter he penned to the Muslim community rejected the “new religion” of moderate Islam. ‘This pen is my gun and these words are my bullets, I fight by these weapons against oppression to promote peace,’ he wrote.

An image on the website appears to show Monis wearing the same headband that photographs suggest he donned during the Martin Place siege, reading: “We are ready to sacrifice for you, O Muhammad.”

Shortly after Tony Abbott’s government was elected in September last year, Monis sent the prime minister a letter inviting him to a live debate in which he said he would prove that “Australia and Australians will be attacked” as a result of the country’s participation in the war in Afghanistan.

Manny Conditsis, a lawyer who represented Monis at one point, has decribed his former client as an isolated figure who might have felt that he had nothing to lose, “hence participating in something as desperate and outrageous as this”.

“His ideology is just so strong and so powerful that it clouds his vision for common sense and objectiveness,” Conditsis told ABC news.