Abubakar Shekau led transformation of Nigeria's Boko Haram

The militant group Islamic State West African Province (ISWAP) said in an audio recording heard by Reuters on Sunday that Abubakar Shekau, leader of rival Nigerian militant Islamist group Boko Haram, was dead.

Following are details about Shekau and Boko Haram.

Boko Haram

The group's name is Jama'atu Ahlis-Sunna Lidda'Awati Wal-Jihad, Arabic for "People Committed to the Prophet's Teachings for Propagation and Jihad". But, because of its teachings, people called it "Boko Haram", which means "Western education is forbidden" in the Hausa language spoken across the north.

Its original members were followers of militant preacher Mohammed Yusuf from the northeastern state of Borno, who wanted wider adoption of Islamic Sharia law across Nigeria.

He died in police custody in 2009. The following year, Shekau, his deputy, announced he was the new leader.

Full-fledged insurgency

Boko Haram became a full-fledged insurgency under Shekau, staging prison breaks and bombings across northern Nigeria. In 2014, they began overrunning northeastern towns in an attempt to create an Islamic state under Sharia law.

By early 2015, Boko Haram controlled a huge swathe of land near Lake Chad before being driven from most of it by troops from Nigeria, Chad, Cameroon and Niger, and South African mercenaries.

More than 30,000 people have been killed and 2 million displaced since the insurgency began in 2009, according to the United Nations refugee agency and the New York-based Council on Foreign Relations think tank.

Violence

Shekau, who had a $7 million bounty placed on his head by the United States, delivered fervent sermons to his followers.

Shekau's suicide bombers attacked not only churches and markets, but mosques too. His group at times sent young girls strapped with bombs into crowded areas.

He held that even other Muslims, if not allied with him, were valid targets. That alienated a local population that sympathised with many of his other causes, such as promoting Islamic teaching and eradicating government corruption.

Boko Haram camps are feral places, say experts and people who spent time with the militants before escaping. A suspicious man, Shekau frequently executed lieutenants.

Chibok girls

His fighters abducted thousands of women for forced marriage and children for use as child soldiers. Women who fled speak of being wedded to insurgents, being made to remarry if a husband died and incessant rape.

Shekau's fighters kidnapped more than 270 schoolgirls from the town of Chibok in 2014, kicking off a global social media campaign fronted by the likes of Michelle Obama and dubbed #BringBackOurGirls.

Around 100 of the Chibok Girls are still missing, and some are thought to have died in captivity.

Fractures

Shekau pledged allegiance to Islamic State in 2015. But the following year it named Abu Musab al-Barnawi as its leader in West Africa.

The move was the result of theological differences after Islamic State told Shekau to cease his wanton killing of civilians, Boko Haram researchers say.

Shekau rejected his demotion.

The two groups split, with Shekau remaining in charge of the faction still known as Boko Haram. Barnawi moved his Islamic State West Africa Province to the shores of Lake Chad, where they would become the dominant insurgency.