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A self-styled sheikh behind a deadly siege at an Australian cafe had "grandiose delusions" and was kicked out of a motorcycle gang because he was deemed too weird, an inquest heard Monday.

Man Haron Monis shot and killed 34-year-old cafe manager Tori Johnson with a sawn-off shotgun following a 17-hour standoff at the Lindt Chocolate Cafe in central Sydney last year.

Iran-born Monis, who was killed by police along with another of his hostages, harbored deep grievances against the Australian government and claimed to be carrying out the December 16 attack as a member of ISIS, the inquest heard.

However, far from belonging to a global movement, it was told of his multiple failed attempts to cultivate a following not just within Sydney's mainstream Muslim community but anywhere that would accept him.

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Monis was on bail at the time of the siege despite facing charges relating to the murder of his ex-wife, who was found burned to death in a Sydney apartment block.

Between 2002-2007 he had reinvented himself as a new-age guru or clairvoyant, marketing his "spiritual healing" techniques to female clients through advertisements in ethnic newspapers.

He was eventually charged with more than 50 counts of sexual and indecent assault as a result of his activities during that period, the inquest heard.

In 2012 or 2013, Monis unsuccessfully attempted to join the notorious Rebels Motorcycle Club, said Sophie Callan, a lawyer assisting the inquiry. He was rejected because the biker gang thought that he was too "weird".

"They took his motorbike," she said.

Monis, who received Australian citizenship after claiming persecution, falsely claimed that his late father had been an ayatollah in Iran, another lawyer Jeremy Gormly told the inquest.

He was found also guilty in 2012 of sending threatening letters to the families of eight Australian soldiers killed in Afghanistan and was known to harass government employees, the inquest heard.

-Reuters