There is little in Ayman al-Zawahiri’s privileged background in a diverse Cairo suburb that foreshadows his emergence as the blood-steeped ideologue who helped Osama bin Laden in his terrorist assault on the West, and who now succeeds him.

In the Maadi neighborhood where his father set up home in 1960, when Zawahiri was 9, there were churches and a synagogue. Wealthy Egyptians and foreigners congregated at the Maadi Sporting Club; although they were never members, Zawahiri’s father took him to the club to watch Disney movies.

Zawahiri, a twin born with a sister in 1951, is the scion of two prominent Egyptian families. His father was a professor of pharmacology, and his maternal grandfather was the president of Cairo University. A great-uncle headed al-Azhar, the most prestigious seat of Islamic scholarship in the Middle East.

Zawahiri was an outstanding student who, under the tutelage of a radical uncle, began to form strong political and religious beliefs at an early age. As a 15-year-old, he formed an underground cell bent on establishing an Islamist state, and his activism intensified at Cairo University, where he studied medicine.

In 1978, after military service, he married Azza Nowair, the daughter of another prominent clan whose religious fervor attracted Zawahiri and alarmed her secular family. At the wedding reception, no music or photographs were allowed, and the sexes were separated, according to Lawrence Wright in his history of al-Qaeda, “The Looming Tower.”

While working at a clinic in Cairo, Zawahiri was invited to go to Pakistan to help treat refugees and Afghan fighters wounded in the growing resistance to the Soviet invasion. Zawahiri made a number of short forays into Afghanistan itself and later wrote how he marveled at the bravery of the mujaheddin.

His own was about to be tested.

The cell Zawahiri founded as a teenager had by then coalesced with other like-minded groups and become Jamaat al-Jihad, or the Jihad Group. A member of the group, who was a junior officer in the Egyptian military, assassinated Egyptian President Anwar Sadat in 1981.

Zawahiri was arrested in the ensuing sweeps. He was subjected to beatings and torture, and a friend and biographer, Montasser al-Zayyat, said the treatment transformed Zawahiri into an unforgiving man of violence. Under duress, he also buckled. While in custody, he set up a friend and fellow conspirator who had until then eluded capture. Zawahiri went on to testify against some of his fellow Islamists.

Later, at a mass trial, he was the unbowed spokesman for the defendants. “We are not sorry,” he told the cameras. “We are here . . . the real Islamic front and the real Islamic opposition against Zionism, communism and imperialism.”

In prison, Zawahiri met Egypt’s leading Islamist, Omar Abdul Rahman, the “blind sheikh” who would be convicted for his role in the first attack on the World Trade Center in 1993. But there was no communion, and the two ambitious men clashed bitterly over who should lead Egypt’s Islamist radicals.

After a three-year trial, Zawahiri was convicted but quickly released for time served. He soon moved to Saudi Arabia, and Zayyat said he fled the country not for fear of further persecution but “because the guilt of betraying his friends weighed so oppressively on his conscience.”

By 1986, Zawahiri had moved on to Peshawar, Pakistan, where he resumed his work as a doctor in the anti-Soviet fight. It is possible that Zawahiri first met bin Laden while in Saudi Arabia, but the two became close in Pakistan, where Zawahiri helped treat the Saudi’s chronic ailments.

In 1997, while in Afghanistan, Zawahiri was involved in orchestrating the worst terrorist attack in Egyptian history — the 45-minute rampage that killed foreign tourists at the Luxor ruins. In Egypt, revulsion over the attacks was profound and decimated whatever support Zawahiri’s Jihad Group had enjoyed.

In the wake of the attack, Zawahiri announced that his group was merging with al-Qaeda. He brought with him his belief in spectacular terrorism. The next year, al-Qaeda launched its first major attack against the United States when suicide bombers struck American embassies in East Africa. Zawahiri was by now bin Laden’s closest adviser and helped oversee the Sept. 11, 2001, attacks.

Zawahiri and bin Laden escaped together as U.S. forces closed in on them at Tora Bora in eastern Afghanistan, according to military documents. Zawahiri’s wife was killed in late 2001 in Afghanistan when U.S. fighter planes struck an al-Qaeda hideout.

Sometime after crossing into Pakistan, probably in 2002, Zawahiri and bin Laden split up for operational reasons. Zawahiri continued through taped messages to exhort al-Qaeda’s dispersed operatives to continue to target the West.

“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.”

Staff researcher Julie Tate contributed to this report.