When the Sept. 11, 2001, plot was hatched, Nasir al-Wuhayshi was serving as Osama bin Laden’s personal assistant in Afghanistan. A half-decade later, after a daring break from a Yemeni prison, Wuhayshi became the architect of the al-
Qaeda affiliate that experts say poses the biggest threat to the United States.

Yet the man at the heart of a terrorism alert that has shut down U.S. embassies in the Muslim world and elsewhere has managed to keep a strikingly low profile in the West. That is likely to change, experts say, as Wuhayshi uses his growing stature to urge the loose network of cells that subscribe to al-Qaeda’s ideology to place greater emphasis on planning attacks on the West, rather than focusing on domestic enemies.

U.S. officials have stressed that much of al-Qaeda, particularly its core in Pakistan, has been severely weakened by a prolonged campaign of drone strikes. In Yemen, drone strikes killed Anwar al-Awlaki, the American cleric whose propaganda inspired other jihadis, in 2011, as well as Wuhayshi’s deputy, Said Ali al-Shihri, this year.

Still, the haste with which U.S. officials have responded to the latest threat, evacuating diplomats and aid workers from Yemen aboard military aircraft, underscores how menacing Wuhayshi’s group — known as al-Qaeda in the Arabian Peninsula — has become.

“He is among the most important individuals in terms of strategy,” said Rita Katz, the director of SITE Intelligence, a Bethesda-based group that tracks extremist organizations. “Al-Qaeda in the Arabian Peninsula very quickly became one of the most prominent affiliates.”

As terror threats and embassy closings come into focus in the Middle East, Nia-Malika Henderson talks to former Ambassador Ryan Crocker about the challenges in the region. (The Washington Post)

Wuhayshi, 36, who was born and raised in central Yemen, was among the young men of his generation who traveled to Afghanistan in the 1990s inspired by bin Laden’s dogmatic ideology and a desire to restore Palestinian control over territory that now includes Israel. Bin Laden found an ally in the Taliban, which held similarly hard-line views, after the Afghan group seized control of Kabul in the mid-1990s. Al-Qaeda established training camps in Afghanistan, luring Muslims with radical views from around the world.

After the attacks of Sept. 11, 2001, as the U.S. military started bombing al-Qaeda hideouts in Afghanistan, Wuhayshi fled from Tora Bora, in the east, to Iran. “There were security circumstances afterwards,” he said in a 2009 interview published on the group’s Web site. “We left Afghanistan, and I went to Iran.”

Officials in Iran detained Wuhayshi and deported him to his native Yemen weeks later “shackled in irons,” the al-Qaeda leader, also known as Abu Baseer, said in the interview.

In February 2006, Wuhayshi was among 23 al-Qaeda members who broke out of a heavily guarded prison in Yemen’s capital, crawling through a tunnel that led to a nearby mosque. The prison break generated consternation in Washington because the escapees included Jamal Badawi, the mastermind of the Oct. 12, 2000, attack on the USS Cole off the coast of Yemen, which killed 17 American sailors.

Wuhayshi spent his first few years on the run rekindling old ties and taking stock of the stunning evolution of al-Qaeda. The group’s core leadership in Pakistan was being targeted by U.S. drones and had largely lost the ability to plot transnational attacks. The Iraq cell had mushroomed into a powerful insurgency that was fighting the U.S. military and Baghdad’s Shiite-led government. The al-Qaeda group in Algeria remained viable, as did an offshoot in Somalia.

In November 2008, al-Qaeda’s then-deputy leader, Ayman al-Zawahiri, issued a video statement in which he gave an important nod to Wuhayshi, who had attracted relatively little attention as he built an al-Qaeda franchise. And in January 2009, Wuhayshi formally announced the creation of al-Qaeda in the Arabian Peninsula, stressing that the group had a solid leadership structure.

As his group was gaining strength, Wuhayshi, who had previously called on devout Muslims to travel to battlefields in Iraq and Afghanistan, shifted strategy. Instead of carrying out jihad abroad, he said, fighters should focus on killing foreigners in Yemen.

“We the soldiers of Islam . . . advise whoever finds a crusader on the [Arabian] Peninsula to kill him by any means,” he said in a statement released in January 2009. “It is shameful to go to Baghdad and Kabul while the infidel desecrates our land, which they are not permitted to enter.”

Wuhayshi’s group attracted sophisticated bombmakers, most notably Ibrahim Hassan al-Asiri, a Saudi man who is credited with designing the “underwear bomb” that nearly brought down a U.S. passenger plane on Christmas Day in 2009.

The group also attracted two Americans. The most prominent was Awlaki, a former Northern Virginia imam who was a source of inspiration to others in the West, including Army Maj. Nidal M. Hasan, who is charged with killing 13 fellow soldiers at Fort Hood, Tex., in 2009. The other, Samir Khan, was the editor of the group’s English-language Inspire magazine, which is al-Qaeda’s most accessible propaganda tool for native English speakers and other likely recruits. Khan was killed alongside Awlaki in the 2011 drone strike, as was Awlaki’s 16-year-old son.

After the death of Wuhayshi’s deputy this year, al-Qaeda in the Arabian Peninsula warned that it would seek revenge. Intercepted communication between Zawahiri and Wuhayshi appeared to signal to U.S. intelligence officials that a serious plot was in the advanced stage of planning. That exchange, as well as other statements from Zawahiri, show how much he has come to value and rely on Wuhayshi, said Seth Jones, a counterterrorism expert at the Rand Corp.

“I think al-Zawahiri appears to be looking at what happens if he is killed,” Jones said. “The U.S. tempo against al-Qaeda leaders in Pakistan has been pretty serious. The bench of people in Pakistan who have legitimacy has narrowed.”