Nigeria's militant Islamist group Boko Haram - which has caused havoc in Africa's most populous country through a wave of bombings - is fighting to overthrow the government and create an Islamic state.
Its followers are said to be influenced by the Koranic phrase which says: "Anyone who is not governed by what Allah has revealed is among the transgressors".
Boko Haram promotes a version of Islam which makes it "haram", or forbidden, for Muslims to take part in any political or social activity associated with Western society.
This includes voting in elections, wearing shirts and trousers or receiving a secular education.
Boko Haram regards the Nigerian state as being run by non-believers, even when the country had a Muslim president.
Boko Haram leader Mohammed Yusuf was killed after his arrest The group's official name is Jama'atu Ahlis Sunna Lidda'awati wal-Jihad, which in Arabic means "People Committed to the Propagation of the Prophet's Teachings and Jihad".
But residents in the north-eastern city of Maiduguri, where the group had its headquarters, dubbed it Boko Haram.
Loosely translated from the local Hausa language, this means "Western education is forbidden".
Boko originally means fake but came to signify Western education, while haram means forbidden.
Since the Sokoto caliphate, which ruled parts of what is now northern Nigeria, Niger and southern Cameroon, fell under British control in 1903, there has been resistance among the area's Muslims to Western education.
Many Muslim families still refuse to send their children to government-run "Western schools", a problem compounded by the ruling elite which does not see education as a priority.
Against this background, the charismatic Muslim cleric, Mohammed Yusuf, formed Boko Haram in Maiduguri in 2002. He set up a religious complex, which included a mosque and an Islamic school.
Boko Haram despises Western education and wants Islamic law imposed
Many poor Muslim families from across Nigeria, as well as neighbouring countries, enrolled their children at the school.
But Boko Haram was not only interested in education. Its political goal was to create an Islamic state, and the school became a recruiting ground for jihadis to fight the state.
In 2009, Boko Haram carried out a spate of attacks on police stations and other government buildings in Maiduguri.
This led to shoot-outs on Maiduguri's streets. Hundreds of Boko Haram supporters were killed and thousands of residents fled the city.
Nigeria's security forces eventually seized the group's headquarters, capturing its fighters and killing Mr Yusuf.
His body was shown on state television and the security forces declared Boko Haram finished.
But its fighters have regrouped under a new leader and in 2010, they attacked a prison in Maiduguri, freeing hundreds of the group's supporters.
Boko Haram's trademark has been the use of gunmen on motorbikes, killing police, politicians and anyone who criticises it, including clerics from other Muslim traditions and a Christian preacher.
The group has also staged several more audacious attacks in different parts of northern Nigeria, showing that it is establishing a presence across the region and fuelling tension between Muslims and Christians.
These include the 2011 Christmas Day bombings on the outskirts of Abuja and in the north-eastern city of Damaturu, a 2010 New Year's Eve attack on a military barracks in Abuja, several explosions around the time of President Goodluck Jonathan's inauguration in May 2011, followed by the bombing of the police headquarters and the UN headquarters in Abuja.
In a 15-minute video posted on YouTube, the group's leader Abubakar Shekau defended the group's targeting of Christians, saying this was revenge for previous attacks on Muslims.
He also said his group would not be defeated by the security forces.
The attacks have raised global concern, with a US Congressional report - released in November 2011 - warning that Boko Haram was an "emerging threat" to the US and its interests.
The report said Boko Haram may be forging ties with al-Qaeda-linked groups in Africa, but the group denies this.
Analysts say northern Nigeria has a history of spawning groups similar to Boko Haram.
The threat will disappear only if the Nigerian government manages to reduce the region's chronic poverty and builds an education system which gains the support of local Muslims, the analysts say.
Boko Haram: Timeline of terror
2009: Hundreds killed when Maiduguri police stations stormed
2009: Boko Haram leader Mohammed Yusuf captured by army, handed to police, later found dead
Sep 2010: Freed hundreds of prisoners from Maiduguri jail
Dec 2010: Bombed Jos, killing 80 people and blamed for New Year's Eve attack on Abuja barracks
2010-2011: Dozens killed in Maiduguri shootings
May 2011: Bombed several states after president's inauguration
June 2011: Police HQ bombed in Abuja
Aug 2011: UN HQ bombed in Abuja
Nov 2011: Co-ordinated bomb and gun attacks in Yobe and Borno states
Dec 2011: Multiple bomb attacks on Christmas Day kill dozens
- BBC African Service