Americans knew him as al-Qaida’s No. 2 leader, the bespectacled, bushy-bearded deputy to Osama bin Laden. But in reality, it was Ayman al-Zawahri’s brains and blood-drenched hands that guided the world’s most notorious terrorist movement.

Al-Zawahri, 71, was killed by the United States, U.S. officials familiar with the matter said on Aug. 1. No other details were immediately made public.

Al-Zawahri had led his own militant group and pioneered a brand of terrorism that prized spectacular attacks and the indiscriminate slaughter of civilians. When he formally merged his group with al-Qaida in the 1990s, he brought along those tactics as well as an expanded vision for attacking the West.

It was al-Zawahri who postulated that defeating the “far enemy” – the United States – was an essential precursor to taking on al-Qaida’s “near enemy,” the pro-Western Arab regimes that stood in the way of the group’s dream of uniting all Muslims under a global caliphate.

“To kill Americans and their allies – civilian and military – is an individual duty for every Muslim who can do it in every country in which it is possible to do it,” al-Zawahri wrote in a 1998 manifesto. Three years later, he would put words into action by helping to plan the Sept. 11, 2001, attacks on the World Trade Center and the Pentagon.

Though lacking bin Laden’s personal charisma, al-Zawahri became the intellectual force behind many of al-Qaida’s grandest ambitions, including its apparently unsuccessful efforts to acquire nuclear and biological weapons. And, after the group’s forced retreat from its base in Afghanistan in early 2002, it was largely al-Zawahri who led al-Qaida’s resurgence in the lawless tribal region across the border in Pakistan, according to longtime observers of the terrorist group.

In his later years, al-Zawahri presided over al-Qaida at a time of decline, with most of the group’s founding figures dead or in hiding and the organization’s leadership role challenged by aggressive upstarts such as the Islamic State.

Al-Qaida’s leader Ayman al-Zawahri on Sept. 2, 2006. Militant Photo via Associated Press, File

He remained the terrorist group’s figurehead but failed to prevent the splintering of the Islamist movement in Syria and other conflict zones after 2011. Rumored to be in ill health, he became known for his long disappearances from public view, interrupted occasionally by the release of essays, books and videotaped sermons that showcased a characteristically dry, pedantic style that seemed ill-suited for the age of social media.

“Zawahri is the ideologue of al-Qaida, a man of thought rather than a man of action,” Bruce Riedel, a former CIA counterterrorism expert and adviser to four U.S. presidents, said in a September interview. “His writings are ponderous and sometimes unbelievably boring.”

As the second decade after 9/11 neared its end, al-Zawahri’s ability to shape events or exert leadership within the widely scattered jihadist movement looked increasingly in doubt, Riedel said. “He is not the charismatic figure that al-Qaida needs,” he said, “and I don’t see anyone else on the horizon who would be.”

Al-Zawahri’s path to becoming one of the world’s most recognized terrorists had an unlikely beginning in an upper-middle-class, religiously diverse Cairo suburb that was home to many of Egypt’s most accomplished families.

Al-Zawahri’s father, Mohammed Rabie al-Zawahri, was a professor of pharmacology, and his maternal grandfather was a president of Cairo University. At the time of al-Zawahri’s birth on June 19, 1951, his hometown of Maadi had a large Jewish population and boasted more churches than mosques.

An earnest, academically gifted youth, he was influenced early in life by one of his uncles, Mahfouz Azzam, an impassioned critic of Egypt’s secularist government, and by the writings of Sayyid Qutb, an Egyptian author and intellectual who became one of the founders of 20th-century Islamist extremism.

According to an account by Lawrence Wright in his Pulitzer Prize-winning book “The Looming Tower,” it was the execution of Qutb by Egypt’s government in 1966 that inspired al-Zawahri, then 15, to organize a group of young friends into an underground cell devoted to the overthrow of Egypt’s government and the establishment of an Islamic theocracy. Al-Zawahiri’s small band of followers eventually grew into an organization known as Jamaat al-Jihad or the Jihad Group.

Even as his political views hardened, al-Zawahri was pursuing a career in the healing arts, earning a degree in medicine from Cairo University and serving briefly as an army surgeon. He eventually opened a practice in a duplex owned by his parents, and he occasionally tended patients at a Cairo clinic sponsored by the Muslim Brotherhood, a Sunni Islamist political opposition group. He married Azza Nowair, the daughter of a wealthy, politically connected Egyptian family, and the couple eventually would have a son and five daughters.

While working at the Muslim Brotherhood clinic, al-Zawahri was invited to make the first of numerous visits to refugee camps along the Afghanistan-Pakistan border. There, he patched up the wounds of mujahideen who were fighting the Soviets in Afghanistan and crossed paths with a charismatic young Saudi, bin Laden.

At the time, however, al-Zawahri was preoccupied with managing his own revolutionary movement. His Jihad Group initiated a series of plots in the early 1980s to assassinate Egyptian leaders and played a role in the slaying of Egyptian President Anwar Sadat on Oct. 6, 1981.

The massive government crackdown that followed landed al-Zawahri in prison, along with hundreds of his followers. Al-Zawahri was released after serving a three-year sentence, but he would later claim in a memoir that he was tortured during his imprisonment, an experience that he said left him more determined to destroy Egypt’s government through force.

During his nomadic years after prison, al-Zawahri traveled frequently to South Asia and increasingly found common cause with the mujahideen and with bin Laden himself, who came to rely on the Egyptian as his personal physician. The Saudi suffered from low blood pressure and other chronic ailments and required frequent glucose infusions. Al-Zawahri’s steadiness in rendering aid in the face of Soviet bombardment in Afghanistan cemented the doctor’s reputation among the mujahideen, as well as a lifelong friendship with bin Laden.

Al-Zawahri made at least one visit to the United States in the 1990s, a brief tour of California mosques under an assumed name to raise money for Muslim charities providing support for Afghan refugees. At the same time, he continued to press his Egyptian followers toward larger and more spectacular attacks at home, believing that such shockingly brutal tactics would command media attention and drown out more-moderate voices that advocated negotiation and compromise.

While living in Afghanistan in 1997, al-Zawahri helped plan a savage attack on foreign tourists at Egypt’s famous Luxor ruins, a 45-minute killing rampage that claimed the lives of 62 people, including Japanese tourists, a 5-year-old British girl and four Egyptian tour guides.

Ordinary Egyptians were repelled by the slaughter, and support for al-Zawahri and his Jihad Group evaporated. Soon afterward, al-Zawahri told followers that operations in Egypt were no longer possible and that the battle was shifting to Israel and its chief ally, the United States. The Jihad Group officially merged with bin Laden’s larger and better-financed al-Qaida, or “The Base.”

Al-Zawahiri was a senior adviser to bin Laden at the time of al-Qaida’s first high-profile terrorist attacks, the 1998 bombings of U.S. embassies in the capitals of Kenya and Tanzania that killed hundreds of people. Three years later, working from al-Qaida’s base in Afghanistan, he helped oversee the planning of what would become one of history’s most audacious terrorist attacks: the Sept. 11 strikes in New York and Washington.

As the Sept. 11 hijackers were dispatched to begin training in U.S. cities, al-Zawahri was put in charge of planning follow-on waves of terrorist attacks intended to further weaken America’s economy and resolve. He launched an ambitious biological weapons program, establishing a laboratory in Afghanistan and dispatching disciples to search for sympathetic scientists as well as lethal strains of anthrax bacteria.

U.S. intelligence officials believe that al-Zawahri’s efforts might well have succeeded, had he not run out of time. Within weeks of the collapse of New York’s World Trade Center towers, a U.S.-backed military campaign drove al-Qaida’s Taliban allies out of power in Afghanistan and forced al-Zawahri to abandon his bioweapons lab.

U.S. bomber aircraft targeted al-Qaida leaders’ offices and homes, including the compound where al-Zawahri lived. His wife was trapped in rubble after the roof collapsed, but she reportedly refused to be rescued out of fear that men would see her without her veil. She was later found dead of hypothermia.

Al-Zawahri fled with bin Laden to Pakistan’s tribal region, where both men – now with bounties of $25 million on their heads – went into hiding to avoid capture. Though there were no confirmed sightings of either man in the following decade, the CIA launched at least two missile strikes inside Pakistan, in 2006 and 2008, that reportedly targeted buildings recently occupied by the Egyptian.

Despite the intense manhunt, al-Zawahri continued to make regular appearances in videos posted on al-Qaida-friendly websites. U.S. officials believe he also continued to direct numerous terrorist operations, including the 2007 siege of the Red Mosque in Islamabad, Pakistan, that resulted in more than 100 deaths.

Though he occasionally sparred with younger extremists over tactics – he argued that mass killings of Muslims in Iraq had undermined support for al-Qaida – he never publicly wavered in his hatred for the West or his support for violent jihad.

“The entire world is our field against the targets of the Zionist Crusade,” he said in a February 2009 video. “And it is not for the enemy to impose on us the field, place, time and way in which we fight.”

The death of bin Laden in May 2o11 thrust al-Zawahri into the No. 1 position, a role for which, in hindsight, he may not have been ideally suited. The Egyptian, with his dry, cerebral style, failed to inspire jihadists as powerfully as bin Laden or younger leaders such as Jordanian Abu Musab al-Zarqawi, founder of the Iraqi insurgency that would later become the Islamic State.

After the start of the Arab Spring uprisings, al-Zawahri sought to assert command over the patchwork of locally-led Islamist groups fighting for dominance in Syria, Iraq and Libya. His effort would ultimately fail.

The leading al-Qaida affiliate in Syria, known initially as the al-Nusra Front, eventually chose to distance itself from the parent organization, refusing to formally accept the al-Qaida brand. The other major faction, the Islamic State, broke with al-Zawahri entirely and drew a public denunciation from him.

In the decade that followed, partisans within both groups would duel over strategy, tactics and even basic beliefs, but rarely, if ever, looked to al-Zawahri for guidance or resolution of their disputes.

By 2020, al-Zawahri had become increasingly distant, contenting himself to write books and essays and only rarely appearing on video. In September 2021, a pro-al-Qaida website released a new video in which the aging al-Zawahri spoke for an hour and, as if to push back on rumors of his death, made pointed references to recent news events.

But al-Zawahri made no mention of the 20th anniversary of the 9/11 attacks, nor did he address the Taliban takeover of Afghanistan in August, just a month before the video surfaced. He did, however, use the occasion to resurrect his fiery rhetoric from the past, calling once again for a renewal of al-Qaida’s violent campaigns against enemies everywhere.

“Just as they have come together from all corners of the world to fight us,” he said in the video, “we must hit them hard everywhere.”

Julie Tate contributed to this report.