As the nation comes to grips with the 16-hour siege that left two captives and Monis dead, there are still unanswered questions as to what motivated Monis.

His chequered life reveals a man who spent years moulding his image, from mystic poet to senior Muslim cleric to spiritual healer and ultimately to self-declared Islamic State hostage-taker.

But in reality, he was a paranoid and lonely man with serious mental health issues.

Monis was born in 1964 under the name Mohammad-Hassan Manteghi Borujerdi as the youngest and only son of five children.

There were early signs that all was not right in his head, with a former classmate telling the New York Times he had never met a crazier person in his life.

Monis reportedly enrolled at Tehran's Imam Sadiq University when he was 18 and would later marry the daughter of a senior university official. They had two children together.

Years later, he was appointed managing director of a travel agency.

The owner of the business told London-based Persian language news outlet Manoto 1 that he gave Monis the job thinking he was a trustworthy and religious man.

He would later regret that decision, after Monis allegedly fled the country in 1995 with $257,000 of his clients' money, leaving behind his wife and two kids.

The cash belonged to about 50 people who were applying for visas to various countries.

Monis managed to reach Australia, via Malaysia, and claimed political asylum in 1996.

He quickly landed a job at a Sydney carpet shop and started getting the word out to the Iranian community that he was a senior Muslim scholar. As part of his PR campaign, he used a grainy video apparently showing him, in full clerical garb, attending a lecture by then speaker of Iran's Parliament, Mehdi Karroubi, to prove his credentials.

The word eventually got out to Granville's growing Afghan community who were looking for a scholar to lead their congregation.

A group of Afghan elders met with Monis at his home and, after becoming convinced that he was in fact a scholar, invited him to speak at a major religious event at Granville Town Hall.

Despite agreeing to speak about religious issues, Monis used his address to launch a fiery tirade against Iran's government.

The event's organisers later confronted Monis with a video of his speech to ask why he went against his word.

Monis was angered by this, declaring that he had a duty to speak out on important political issues.

"That's when we stopped our contacts with him," an Afghan community member, who asked not to be named, said.

Despite never again delivering a lecture to the Shiite community, Monis uploaded his Granville lecture footage on to YouTube as evidence that he was a prominent scholar in the Sydney community.

"He made it out that he had hundreds of followers and gained a lot of attention in the media through it," a man who knew him at the time said.

"He even started saying that he was an Ayatollah [a senior Shiite cleric]."

Iranian authorities in 2000 launched a bid to have him extradited to face his embezzlement charges but Australia turned down the request as the two countries don't have an extradition agreement in place.

The Iranians have now pointed out the Lindt cafe siege may never have happened had Australian authorities co-operated with their request more than a decade ago.

Around the same time, he started to stage what would become regular public protests around Sydney's CBD, demanding publicity for his so-called political persecution and for his family to be brought to Australia.

When his antics were ignored, he turned to even more bizarre tactics to generate attention, penning offensive letters to the families of dead Australian soldiers in 2008.

His mental state appeared to spiral further in the next few years when he was charged with dozens of sexual assault charges dating back to 2002 when he posed as a "spiritual healer". His therapeutic "services" allegedly involved touching the breasts of women and painting liquid on them.

Monis was also arrested for being an accessory before and after the fact to the grisly murder of his former partner and mother of two of his children, Noleen Pal, whose body was set alight.

Throughout his public antics and his court battles, an increasingly isolated Monis maintained he was the real victim, claiming he had been persecuted by the government and mistreated in prison.

Days before he took over the Lindt cafe, he used his website to rail against Australia for its "terrorism" and declared he had abandoned his previous Shiite faith and embraced a radical version of Sunni Islam.

Last Friday, Monis came before the High Court again for an unsuccessful application to have his conviction for sending the threatening letters to soldiers overturned.

But as his past suggests, Monis's fragile mental state, and not any purported ideology, was behind his bizarre, and ultimately deadly, actions. AAP