What to know about Al-Qaeda leader Ayman al-Zawahiri

Al Qaeda leader Ayman al-Zawahiri killed by US drone strike in Kabul, Afghanistan on Sunday, July 31, was a man who led a life of secrecy and violence.

US President Joe Biden on Monday said the killing of al-Zawahiri,71, an Egyptian-born surgeon-turned-jihadist, was a long-sought "justice".

"He will never again, never again, allow Afghanistan to become a terrorist safe haven because he is gone and we're going to make sure that nothing else happens," said Biden, adding: "This terrorist leader is no more."

Al-Zawahiri and Osama Bin Laden, also killed in May 2010 after a US Navy SEAL team raided his compound in Abbottabad, Pakistan, were on the US list of "most wanted terrorists" for their roles in the 9/11 attacks.

During the attacks, four coordinated suicide terrorist attacks were carried out by the militant extremist network al-Qaeda against the United States on September 11, 2001.

Al-Zawahiri was widely portrayed as Al Qaeda's intellectual spine - its chief operating officer, public relations executive, and a profound influence, who helped the Saudi-born Bin Laden develop from a charismatic preacher into a lethal terrorist with global reach.

From his teenage years in an affluent Cairo suburb, al-Zawahiri led a cat-and-mouse existence, serving prison sentences in Egypt and Russia while being pursued by adversaries, including US counterterrorism authorities who placed a $25 million bounty on his head.

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

He was imprisoned in Egypt for three years for militancy and was involved in the assassination of President Anwar Sadat in 1981 and the massacre of foreign tourists in Luxor in 1997.

He then joined bin Laden in Afghanistan, becoming Al-chief Qaeda's strategist and bin Laden's personal doctor.

He was one of five signatories to bin Laden's "fatwa" in 1998, which called for attacks on Americans. He, like bin Laden, vanished after the September 11, 2001 attacks, surviving multiple assassination attempts and reappearing after reports that he had died.

However, he remained in the sights of the US, with a $25 million bounty on his head for the 1998 Africa attacks. After US Navy SEALs killed bin Laden in 2011, Zawahiri assumed command of Al-Qaeda.

During the decade in which the 71-year-old presided over the group, however, it never regained its prominence as the aggressive Islamic State group took the lead in the jihadist movement, seizing large swaths of territory in Iraq and Syria and declaring a caliphate.