Ayman al-Zawahri, the new leader of the al-Qaida terror network, was born into a life of comfort in Egypt but shaped by life experiences into a feared radical Islamic terrorist.

He is a surgeon by training but an ideological firebrand by choice. Now he is replacing Osama bin Laden, who was killed last month by U.S. commandos in a raid on his Pakistani hideout.

Zawahri was bin Laden's deputy, supporting al-Qaida with his organizational and tactical skills, the first to espouse the use of suicide bombings and independent terror cells. His jihad, or holy war mission, was simple and straightforward — inflict “as many casualties as possible” on the Americans and their allies, especially Israel.

Now he is believed to be living somewhere in the mountainous region near the Afghan-Pakistani border, with the U.S. offering a $25 million reward for information leading to his capture. In regular videotapes, he has condemned the U.S., saying that al-Qaida's fight will not be ended until the Western powers leave “the lands of the Muslims.”

He was born in Cairo to a wealthy family of doctors and scholars and became involved with radical Islam as a teenager. Like many educated young Egyptians, he was outraged at the treatment of Islamists in the 1960s as Egypt moved toward a Soviet-style state under socialist Gamel Abdel Nasser. Thousands of people suspected of subversion were thrown in jail. His sense of shame was only heightened as Israel defeated Egypt in the 1967 war.

While earning a medical degree, he helped to form the Egyptian Islamic Jihad militant group.

Zawahri traveled to Pakistan for the first time in 1980, working with the Red Crescent Society in the city of Peshawar to provide medical treatment to Afghans wounded in fighting with Soviet troops occupying neighboring Afghanistan. He also made his first trips into Afghanistan that year.

Later, he was one of hundreds tried for links to the 1981 assassination of Egyptian President Anwar Sadat. He was acquitted of that, but served a three-year term for illegal arms possession. After his release in 1984, Zawahri returned to Peshawar to support the Afghan insurgency against the Soviets and formed a bond with bin Laden, serving as his personal doctor.

In 1998, Zawahri formed an alliance with bin Laden, becoming his deputy. The United States accuses the Egyptian of helping to organize the bombings of U.S. embassies in Kenya and Tanzania later that year.

Zawahri also is suspected of playing a major role in the 2001 terrorist attacks on the United States, for which al-Qaida claimed responsibility from its base in Afghanistan. He went into hiding with bin Laden when U.S.-led forces invaded Afghanistan weeks later, ousting the country's Taliban militant rulers, who had sheltered the terror network.

Zawahri's hatred of the U.S. also became personal: A U.S. air strike killed the Egyptian's wife and at least two of his children in southern Afghanistan's Kandahar province in December 2001.

Zawahri proceeded to rebuild al-Qaida in the lawless tribal regions of the Afghan-Pakistani border and became the new face of the terror network, releasing videos and audiotapes taunting the United States as bin Laden faded from view.

In some videos, the bearded Zawahri could be seen jabbing his finger and staring from behind heavy-rimmed glasses. The Central Intelligence Agency came close to killing or capturing him several times in the Pakistani tribal region.

But he remains at large and now, as he turns 60 later this week, has become the head of al-Qaida.