Who was al-Qaeda leader Ayman al-Zawahri

A U.S. drone strike in Afghanistan killed Ayman al-Zawahri, who helped Osama bin Laden plot the Sept. 11, 2001, attacks on the United States and helped al-Qaeda survive and spread in the years after

An Egyptian, al-Zawahri was born June 19, 1951, to a comfortable family in a leafy, drowsy Cairo suburb.

Religiously observant from boyhood, he immersed himself in a violent branch of a Sunni Islamic revival that sought to replace the governments of Egypt and other Arab nations with a harsh interpretation of Islamic rule.

Al-Zawahri worked as an eye surgeon as a young adult, but also roamed Central Asia and the Middle East, witnessing Afghans' war against Soviet occupiers in that country, and meeting young Saudi Osama bin Laden and other Arab militants rallying to help Afghanistan expel Soviet troops.

He was one of hundreds of militants captured and tortured in Egyptian prison after Islamic fundamentalists' assassination of President Anwar Sadat in 1981. Biographers say the experience further radicalized him. Seven years later, al-Zawahri was present when bin Laden founded al-Qaeda.

Also watch: Why killing of al Qaeda's Ayman al-Zawahri is important in fight against terror

Al-Zawahri merged his own Egyptian militant group with al-Qaeda. He brought al-Qaeda organisational skill and experience — honed underground in Egypt, evading Egyptian intelligence — that allowed al-Qaeda to organize cells of followers and strike around the world.