Al Qaeda leader Ayman al-Zawahiri, 71, was a key architect behind multiple assaults on the US and was "deeply involved" in the planning of the September 11, 2001 attacks that killed 3,000 people. Born in 1951, he grew up in Egypt's upper-class neighbourhood. Zawahiri, a trained surgeon, became al Qaeda's leader after Osama bin Laden was killed in 2011.