Martin Place, Sydney siege gunman identified as Man Haron Monis

The man who held more than a dozen people hostage, placing Sydney's CBD into lockdown is no stranger to the NSW police or the judiciary.

Self-described cleric, Man Haron Monis, 50, first came to attention of police when he penned poisonous letters to the family of dead Australian soldiers seven years ago.

Last year he was charged with being an accessory to the murder of his ex-wife and mother of two.

Most recently, he was charged with more than 50 allegations of indecent and sexual assault relating to time allegedly spent as a self-proclaimed "spiritual healer" who dealt with black magic at a premises in western Sydney more than a decade ago.

Monis, who has also gone by the names of Sheikh Haron and Mohammad Hassan Manteghi, was born in Iran and most recently has been living at Bexley North in Sydney's south.

He recently likened himself on his own webpage to Wikileaks founder Julian Assange, claiming the most recent charges against him have been laid for "political reasons".

His website also carries a quote, posted earlier this month stating: "I used to be a Rafidi, but not any more. Now I am a Muslim, Alhamdu Lillah".

It has been Monis' on-going legal battle for his conviction for penning the poisonous letters to the families of dead Australian soldiers between 2007 and 2009 that has consumed him.

It is understood Monday's incident followed an unsuccessful, last-ditch attempt in the High Court on Friday to have the charges overturned.

Monis was sentenced to 300 hours of community service and placed on a two year good behaviour bond for the "offensive and deplorable letters" sent with the assistance of his girlfriend Amirah Droudis.

They were sent to the families of  Private Luke Worsley and Lance Corporal Jason Marks, who were killed in Afghanistan in 2007 and 2008.

He also sent a letter in 2009 to the family of the Austrade official Craig Senger, who was killed in the bombing of the Marriott Hotel in Jakarta in 2007.

Monis claimed the letters were his own version of a "flower basket" or "condolence card".

Bree Till, widow of Sergeant Brett Till, killed while defusing a bomb on March 12, 2009, said at the time of his conviction: "We sat reading these letters (which) made out to be something supportive but then the juxtaposition of this man accusing my husband of being a child-killer while dictating how I should raise my children. It was scary," she said.

He fought the validity of the charges all the way to the High Court arguing they were political and only sought to persuade the families to oppose Australia's military involvement in Afghanistan.

But when he lost that battle, and had to stand trial, he pleaded guilty to all 12 charges against him in August 2013.

But his problems with the law did not end there. Monis is currently on bail in relation two separate, serious cases.

He was charged in November 2013 with being an accessory before and after the fact to the murder of his ex-wife Noleen Hayson Pal.

Ms Pal was stabbed and set alight in a Werrington apartment block.

Droudis has been charged with the murder.

And then in April this year, Monis was charged by sex crimes squad detectives with the indecent and sexual assault of a woman in western Sydney in 2002.

Police allege that Monis was a self-proclaimed "spiritual healer" who operated out of premises on Station Street at Wentworthville.

News of his arrest prompted more victims to come forward and Monis was hit with an additional 40 charges in October.

It is alleged that Monis placed ads in local newspapers offering "spiritual consultation".

He claimed to be an expert in astrology, numerology, meditation and black magic.

Monis has posted online that the police charges are part of a witch hunt against him.

"Since the Australian government cannot tolerate Sheikh Haron's activity, is trying to damage his image by these false accusations, and also for putting pressure on him to stop his activity and keep him silent, but God willing Man Haron Monis will not stop his political activity against oppression," he writes in a description of himself on his website, sheikhharon.com

His former Facebook page, pulled down on Monday night as the siege continued had 14,725 "likes" when it was shut down.