Ayman al-Zawahiri, who has been killed in a US drone strike in Afghanistan, was a key ideologue behind the global terror network for several decades.

Here are 5 facts about him:

1. Zawahiri grew up in a comfortable household in Cairo. He became involved with Egypt's radical Islamist community at a young age and was reportedly arrested at 15 for joining the outlawed Muslim Brotherhood.

2. He was jailed for three years in Egypt for militancy and implicated in the 1981 assassination of president Anwar Sadat and the massacre of foreign tourists at Luxor in 1997. He then linked up with bin Laden in Afghanistan, becoming Al-Qaeda's main strategist and serving as bin Laden's personal doctor.

3. He was one of five signatories to bin Laden's 1998 "fatwa" calling for attacks against Americans. Like bin Laden, he vanished after the September 11, 2001 attacks, surviving repeated attempts on his life and re-emerging after reports that he had already died.

4. But he stayed in US sights, with a $25 million bounty on his head for the 1998 Africa attacks. Zawahiri took command of Al-Qaeda in 2011 after US Navy SEALs killed bin Laden.

5. But during the decade the 71-year-old presided over the group, it never recovered its prominence, as the aggressive Islamic State group took the lead in the jihadist movement, seizing large swathes of territory in Iraq and Syria and declaring a caliphate.