ABUJA, Nigeria—When he appeared in a video on Monday boasting of having abducted more than 200 schoolgirls, the leader of terror group Boko Haram took the occasion to egg on the U.S. Army and get in a dig at ancient Egypt.
"We don't fear any American troops," shouted Abubakar Shekau, whose Islamist insurgency has terrorized northern Nigeria and recently drawn search-and-rescue advisers from the U.S. and other countries. "Let even the Pharaoh himself be sent down here! We will deal with him squarely!"
Now, Mr. Shekau, believed to be in his late 30s or early 40s, is finally getting a perverse kind of recognition—even becoming America's most wanted man in Africa. The $7 million bounty offered by the U.S. State Department is the largest ever offered for a single individual on the continent.
Mr. Shekau has achieved this ignominious rank through a willingness to slaughter. Boko Haram has killed more than 7,000 people in the past two years alone, according to the Council on Foreign Relations. Most of the group's victims are Muslims deemed too close to the Nigerian state or insufficiently devout. Boko Haram loosely means "Western Education is a Sin" in the local Hausa language.
"Even his mother—his own mother—said he was insane," said the adviser. "They are not on speaking terms." Mr. Shekau's mother couldn't be located for comment.
U.S. officials also see Mr. Shekau as mentally unstable.
"Any impartial observer—especially those who have watched his public statements over the years—would be left wondering about Shekau's mental state, especially after his most recent video appearance," the U.S. counterterrorism official said.
In his latest speech, Mr. Shekau pointed out that in the international outrage over the kidnapped girls, no notice has been paid to his abduction of three times as many boys in the past year. "Why is the world not talking about that?" he asked.
His video diatribes often veer into the absurd. He has shouted threats against Margaret Thatcher, the late British prime minister. In a tape released in April, he called Abraham Lincoln an infidel three times. Queen Elizabeth II also is a recurring target of his harangues.
He also issues instruction to fellow jihadis across Nigeria. "Just pick up your knife, break into homes and kill," he demanded in a message in January. "Slaughter anyone in their sleep you come across."
With the abduction of the schoolgirls, news organizations and social media beyond Nigeria finally gave Mr. Shekau the attention he believes he merits.
"A poor guy from Maiduguri, he never thought that the U.S. president would be calling him [out] by name," said Fatima Akilu, director of behavioral analysis in the office of Nigeria's national security adviser. "He's on the lips of everybody and he can't believe his luck. And he will continue to hit out wherever he can to keep himself relevant."
Mr. Shekau has frequently welcomed efforts to hunt him down. "You can see I'm a radical!" he said in a video last year. "You should kill me!"