Story highlights Analysts describe Shekau as a loner and a master of disguise

When he came to power, he vowed to strike back against the military

He uses Islam to recruit the disenfranchised

The U.S. has placed a bounty on his head

He is the face of terror. A ruthless leader with a twisted ideology. And the sadistic architect of a campaign of mayhem and misery.

And yet, very little is known about Abubakar Shekau, the leader of Boko Haram.

He operates in the shadows, leaving his underlings to orchestrate his repulsive mandates. He resurfaces every once in a while in videotaped messages to mock the impotence of the Nigerian military. And he uses his faith to recruit the impressionable and the disenfranchised to his cause.

He's a religious scholar

Shekau was born in Shekau village that borders Niger. He studied under a cleric and then attended Borno State College of Legal and Islamic Studies for higher studies on Islam.

JUST WATCHED Kidnapper: Allah says to sell girls Replay More Videos ... MUST WATCH Kidnapper: Allah says to sell girls 01:43

Photos: Photos: Nigerians protest over kidnapped girls Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Police in riot gear block a route in Abuja, Nigeria, on Tuesday, October 14, during a demonstration calling on the Nigerian government to rescue schoolgirls kidnapped by the Islamist militant group Boko Haram. In April, more than 200 girls were abducted from their boarding school in northeastern Nigeria, officials and witnesses said. Hide Caption 1 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Women in Abuja hold a candlelight vigil on Wednesday, May 14, one month after the schoolgirls were kidnapped. Hide Caption 2 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – People march in Lagos, Nigeria, on Monday, May 12, to demand the release of the kidnapped schoolgirls. Hide Caption 3 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Catholic faithful in Abuja take Holy Communion and pray for the safety of the kidnapped schoolgirls on Sunday, May 11. Hide Caption 4 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Catholic faithful attend a morning Mass in honor of the kidnapped schoolgirls in Abuja on May 11. Hide Caption 5 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Catholics nuns pray in Abuja on May 11. Hide Caption 6 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – A woman attends a demonstration Tuesday, May 6, that called for the Nigerian government to rescue the girls. Hide Caption 7 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Community leader Hosea Sambido speaks during a May 6 rally in Abuja. Hide Caption 8 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Brig. Gen. Chris Olukolade, Nigeria's top military spokesman, speaks to people at a demonstration May 6 in Abuja. Hide Caption 9 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Women march Monday, May 5, in Chibok, Nigeria. Hide Caption 10 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – People rally in Lagos on Thursday, May 1. Hide Caption 11 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Police stand guard during a demonstration in Lagos on May 1. Hide Caption 12 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Protesters take part in a "million-woman march" Wednesday, April 30, in Abuja. Hide Caption 13 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Obiageli Ezekwesili, former Nigerian education minister and vice president of the World Bank's Africa division, leads a march of women in Abuja on April 30. Hide Caption 14 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – A woman cries out during a demonstration in Abuja on Tuesday, April 29, along with other mothers whose daughters have been kidnapped. Hide Caption 15 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – A man weeps as he joins parents of the kidnapped girls during a meeting with the Borno state governor in Chibok on Tuesday, April 22. Hide Caption 16 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Mothers weep April 22 during a meeting with the Borno state governor in Chibok. Hide Caption 17 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Four female students who were abducted by gunmen and reunited with their families walk in Chibok on Monday, April 21. Hide Caption 18 of 19 Photos: Photos: Nigerians protest over kidnapped girls Nigerians protest over kidnapped schoolgirls – Borno state Gov. Kashim Shettima, center, visits the girls' school in Chibok on April 21. Hide Caption 19 of 19

JUST WATCHED Nigeria: The Slavery Connection Replay More Videos ... MUST WATCH Nigeria: The Slavery Connection 02:18

JUST WATCHED Parents doubt Nigerian government Replay More Videos ... MUST WATCH Parents doubt Nigerian government 00:53

Map: Where the girls were kidnapped

That's why he's also known as 'Darul Tawheed,' which translates to an expert in monotheism, or the oneness of Allah.

He's a polyglot

He speaks several languages fluently: Hausa, Fulani, Kanuri and Arabic. But English isn't one of them. After all, he heads a group that rejects all things Western.

He's elusive

Even his age is unknown -- estimates range between 38 and 49.

He's a loner

Analysts describe Shekau as a loner and a master of disguise. He does not speak directly with members, opting to communicate through a few select confidants.

He uses many aliases: Abu Bakr Skikwa, Imam Abu Bakr Shiku and Abu Muhammad Abu Bakr Bin Muhammad Al Shakwi Al Muslimi Bishku among them.

He was an unruly No. 2

Boko Haram was founded by Mohammed Yusuf, a charismatic, well-educated cleric who drove a Mercedes as part of his push for a pure Islamic state in Nigeria. He wasn't too effective as a leader and had a hard time keeping his second-in-command in check. Shekau was more radical and had grander designs.

... And merciless as No. 1

Mohammed Yusuf was killed in a security crackdown in 2009, along with about 700 of his followers. That left Shekau in charge. He vowed to strike back, and his group has spared no one: government workers, police officers, journalists, villagers, students and churchgoers. Human Rights Watch estimates that in the past five years, more than 3,000 people have been killed.

JUST WATCHED Nigerian father: 'We sleep in the bush' Replay More Videos ... MUST WATCH Nigerian father: 'We sleep in the bush' 00:29

JUST WATCHED More schoolgirls abducted in Nigeria Replay More Videos ... MUST WATCH More schoolgirls abducted in Nigeria 02:29

He's come back from the dead

The Nigerian military has touted Shekau's death several times, only to retract its claim after he appeared alive and vibrant in propaganda videos.

They almost got him in September 2012 when they raided his home, where he had snuck in for his six-day-old baby's naming ceremony, according to the International Crisis Group . He managed to get away with a gunshot wound to the leg; his wife and three children were taken by the military.

He uses Islam to recruit and radicalize

The northeast, where Boko Haram has been most active, is economically depressed and among the least educated regions in Nigeria. Shekau has done a good job of convincing residents that the powers in Abuja are corrupt and a better system of government would be a strict enforcement of Islamic Sharia law across Nigeria. And his promise, coupled with a weapon and a license to plunder, has been enticing to hundreds of young men.

... and the government's response isn't helping

The central government's heavy-handed and frequently untargeted anti-terrorism campaign has just helped create more members to sustain Boko Haram. The country's own Human Rights Commission last year accused the military of arbitrary killings, torture and rape in its campaign against the group. This makes for fertile territory for Boko Haram.

He's exporting his brand of terror

There's no firm evidence as yet that Boko Haram has ambitions beyond Nigeria. But its campaign of terror has spilled into remote parts of Cameroon and it appears to have informal links with militant Islamist groups in Mali and Niger.

He's made good on his brutal threat

It was in May 2013 that Shekau first announced in a video that Boko Haram would start kidnapping girls. The kidnappings, he said, were retaliation for Nigerian security forces nabbing the wives and children of group members.

The most horrifying instance was last month's abduction of 276 girls from a girl's school.

"I abducted your girls," he taunted with a chilling smile in a new video that surfaced this week . "There is a market for selling humans. Allah says I should sell. He commands me to sell."

There's a $7 million bounty on his head

Shekau has been on the radar of U.S. officials since he came to power in 2009. Last June, the United States put a bounty on him, offering a reward of up to $7 million for information leading to his location.

... But that's yet to yield results

Here's why, says CNN's Chief International Correspondent Christiane Amanpour: "(African warlord) Joseph Kony's had a bounty for years and years. Even with the 'Stop Kony' video that went viral, nothing has happened to get Joseph Kony -- even though it's about the only thing in Africa that the United States has committed some forces and some intelligence to.

"Osama bin Laden was not given up because of the $25 million bounty. And who knows whether this will be the case."