The gunman holding dozens of people hostage in a Sydney cafe has been named by police as Iranian-born radical Muslim cleric Man Haron Monis.

Born Manteghi Bourjerdi, Monis fled Iran in 1996 and was granted asylum in Australia, where he changed his name.

The cleric, who does not enjoy the support of mainstream Muslims, has previously gained media attention for a hate mail campaign, where he sent offensive letters to the families of dead Australian soldiers in protest of the presence of Australian troops in Afghanistan, according to 9News.

In 2009, Monis was sentenced to 300 hours community service for his hate mail campaign, which he carried out with his partner Amirah Droudis.

In 2013, Monis was investigated by police but not charged for allegedly organising the murder of his ex-wife Noleen Pal, who had been stabbed to death and her body set alight in a Werrington apartment block.

In April 2014, Monis was charged with sexually assaulting seven women while working as a spiritual healer Wentworthville where he claimed to be an expert in meditation and black magic.

In October, Monis was charged with a further 40 sexual offences in relation to his work as a spiritual healer, and is due to appear in court in February 2015.