Egyptian-born doctor and surgeon Ayman al-Zawahri is al Qaeda's No. 2 leader likely to succeed Osama bin Laden, who was killed in a US-led operation.
Following are some key facts about Zawahri:
* Zawahri is described as the chief organizer of al Qaeda and al Qaeda leader Osama bin Laden's closest mentor.
* Zawahri and bin Laden met in the mid-1980s when both were in the northwestern Pakistani city of Peshawar to support mujahideen guerrillas fighting the Soviets in Afghanistan.
* Born in 1951 to a prominent Cairo family, Zawahri was the son of a pharmacology professor and grandson of the grand imam of Al Azhar, one of the most important mosques in the Arab world.
* He graduated from Egypt's most prestigious medical school in 1974.
* When the militant Egyptian Islamic Jihad was founded in 1973, he joined. When members posed as soldiers and assassinated President Anwar Sadat in 1981, he was among 301 people arrested. He went on trial but was cleared of involvement in Sadat's death. He did, however, spend three years in jail for possession of an unlicensed pistol.
* Zawahri has broadcast dozens of messages since the Sept. 11 attacks on the United States in 2001. In the latest monitored by the SITE Intelligence Group last month, he urged Muslims to fight NATO and American forces in Libya.
* In Jan. 2006 Zawahri blasted US President George W Bush as a "butcher" in a video tape, saying a recent US air strike targeting him had killed only innocent people. Earlier in the month, Pakistani intelligence sources said four top al Qaeda militants were believed to be killed in a US air strike, which US officials say was aimed at Zawahri.