Abubakar Shekau is the leader of the Nigerian militant Islamist group Boko Haram, which been behind a deadly insurgency in the north-east of the country for the last five years. Nigeria analyst Abdullahi Tasiu Abubakar looks at the country's most-wanted man, who has been designated a terrorist by the US government.
Boko Haram's leader is said to be a fearless loner, a complex, paradoxical man - part-theologian, part-gangster.
Since he took over, Boko Haram has become more radical and carried out more killings.
Perhaps the most shocking revelation about him was the video clip of him laughing as he admitted the abduction of more than 200 schoolgirls in April 2014, promising to sell them.
"I abducted your girls," he said. "I will sell them in the market, by Allah. I will sell them off and marry them off."
Fondly called imam or leader by his followers, Abubakar Muhammad Shekau was born in Shekau village in Nigeria's north-eastern state of Yobe.
Some say he is in his late 30s, others believe he is in his mid-40s - the uncertainty adds to the myths surrounding him.
The US government has offered a reward of up to $7m (£4.6m) for information about his location.
Radical theology student
Shekau was once said to have been killed by security forces in 2009 - only for him to reappear in videos posted on the internet less than a year later as Boko Haram's new leader.
Similar subsequent claims of his death also turned out to be false.
The group's founder, Muhammad Yusuf, died in police custody in July 2009, and hundreds of others were killed during that massive crackdown - which many blame for making the group even more violent.
Shekau has not been seen in public since.
Instead, still images and video clips of him are released from time to time, mostly online, by the group's faceless "public enlightenment department".
Shekau is said to have met his predecessor in Maiduguri, capital of Borno state and Boko Haram's then-stronghold, through a mutual friend, Mamman Nur.
Nigeria's authorities say Nur masterminded the August 2011 bombing of the UN office complex in Nigeria's capital, Abuja.
All three were theology students - and Shekau was seen as the quietest and perhaps the most radical of them.
"He hardly talks, he is fearless," says Ahmed Salkida, a journalist with such good access to Boko Haram that, at one stage, he was suspected of being a member.
He says he only escaped summary execution by police in Maiduguri after an intelligence officer intervened.
"He is one of those who believes that you can sacrifice anything for your belief," Mr Salkida says.
'Aping of Osama Bin Laden'
Shekau is fluent in his native Kanuri language, as well as Hausa and Arabic. He now also adds English sentences in the tapes his group releases to journalists.
When Muhammad Yusuf was killed, Shekau is said to have married one of his four wives and adopted their children - perhaps, say sources who do not want to be named, to preserve Boko Haram's cohesion or "purity".
The group has a highly decentralised structure - the unifying force appears to be ideology, though many believe that they are now more interested in vengeance than in ideology.
Shekau does not communicate directly with the group's foot soldiers - he is said to wield his power through a few select cell leaders, but even then contact is minimal.
"A lot of those calling themselves leaders in the group do not even have contact with him," Mr Salkida says.
Shekau has neither the charismatic streak nor the oratorical skills of his predecessor - but he has an intense ideological commitment and ruthlessness, say people who study the group.
"He is the leader of the more militant wing of the group as testified by his aping of Osama Bin Laden in his video appearances," says Abubakar Mu'azu from the University of Maiduguri.
Shekau issued a chilling message in one of those appearances - which provides a major insight into what his leadership of the group will bring.
"I enjoy killing anyone that God commands me to kill - the way I enjoy killing chickens and rams," he said in the video clip released just after Boko Haram had carried out one of its deadliest attacks, in January 2012, killing more than 180 people in Kano, northern Nigeria's largest city.
Boko Haram at a glance
- Founded in 2002
- Initially focused on opposing Western education - Boko Haram means "Western education is forbidden" in the Hausa language
- Launched military operations in 2009 to create Islamic state
- Thousands killed, mostly in north-eastern Nigeria - also attacked police and UN headquarters in capital, Abuja
- Some three million people affected
- Declared terrorist group by US in 2013
Shekau is also the group's spiritual leader - and, judging by video footage, he seems equally comfortable delivering sermons to his followers.
"He has a photographic memory and is well-versed in theology," Mr Salkida said.
His followers nickname him "Darul Tawheed", which translates as a specialist in Tawheed. This is an orthodox doctrine of the uniqueness and oneness of Allah, which is the very cornerstone of Islam.
But Nigeria's mainstream Muslim clerics do not regard Shekau as a scholar and question his understanding of Islam.
They regularly condemn the bombings and drive-by shootings committed by his followers against anyone who disagrees with them.