ISLAMABAD, Pakistan, June 16, 2011 (AFP) - Ayman al-Zawahiri, named Thursday as the new leader of Al-Qaeda, is an Egyptian surgeon considered the brains behind the global terror franchise but bereft of the potent charisma of Osama bin Laden.
(FILES) This image provided by SITE Intelligence Group shows Ayman al-Zawahiri as he gives a eulogy for fellow al-Qaeda leader Osama bin Laden in a video released on jihadist forums on June 8, 2011.
The 59-year-old eye doctor, who grew up in a comfortable household in Cairo before he turned to dissident politics and then terrorism, is now cemented as Washington's most-wanted terrorist with a $25 million reward for his capture.
Like bin Laden, he vanished after the September 11, 2001 attacks. But unlike the Saudi, whose decade on the run ended when US Navy SEALs swooped on his Pakistani home, killing him at point-blank range, Zawahiri is still at large.
In an online statement, Al-Qaeda said that under Zawahiri it would pursue jihad (holy war) against the United States and Israel "until all invading armies leave the land of Islam".
With organisational skills, cunning and intelligence said by analysts to eclipse that of bin Laden, he has reportedly not been seen since October 2001, at that time in Afghanistan, close to the Pakistan border.
From hiding, Zawahiri has issued video missives calling for war on the West. The most recent was a filmed eulogy to bin Laden, vowing to pursue jihad in a tape reported by the SITE Intelligence Group on June 8.
It was a message of loyalty to bin Laden, who analysts believe alone had the charisma capable of uniting an increasingly disparate group divided between Egyptians and non-Egyptian Arabs.
"The man who terrified America in his life will continue to terrify it after his death," Zawahiri said in the message posted on jihadist online forums, decked out in white garb and a turban with a machine-gun behind him.
Although Zawahiri had long been bin Laden's presumed successor, US officials present him as a far less potent threat.
"Our assessment is that he is not anywhere near the leader that Osama bin Laden was," White House National Security Advisor Tom Donilon said in May.
Some within Al-Qaeda see Zawahiri as given to meddling or "micro-managing", a US intelligence official said a few days later.
"If free and fair elections were held, Zawahiri most likely would have a fight on his hands," the official said.
While bin Laden was Al-Qaeda's inspiration, his deputy is believed to be the main strategist -- the real mastermind who steered operations, including the September 11 attacks, as well as bin Laden's personal doctor.
It was often up to Zawahiri -- identifiable by a prominent lump on his forehead -- to motivate the group's followers with his hectoring video appearances, jabbing his finger and staring from behind heavy-rimmed glasses.
Zawahiri's father was a renowned physician and his grandfather a prayer leader at Cairo's Al-Azhar institute, the highest authority for Sunni Muslims.
He became involved with Egypt's radical Muslim community at a tender age and was reportedly arrested as young as 15 for being a member of the outlawed Muslim Brotherhood, the Arab world's oldest fundamentalist group.
He has published several books and pamphlets on Islamic fundamentalism, which came for many to symbolise the radical Islamist movement.
He was jailed for three years in Egypt for militancy and was implicated in the 1981 assassination of president Anwar Sadat and the massacre of foreign tourists at the city of Luxor in 1997.
Facing a death sentence, he left Egypt in the mid-1980s initially for Saudi Arabia, but soon he headed for Pakistan's northwestern city of Peshawar where the resistance to the Soviet occupation of Afghanistan was based.
It was at that time, when thousands of Islamist fighters flooded into Afghanistan during the 1980s, that Zawahiri and bin Laden met.
He worked as a doctor treating wounded fighters and linked up with Arab Islamist militants who came to take part, including bin Laden.
In the early 1990s Zawahiri is believed to have lived in Europe before joining bin Laden in Sudan or Afghanistan.
In 1998 he was one of five signatories to bin Laden's "fatwa" calling for attacks against Americans and he began appearing regularly at the Al-Qaeda leader's side.
He is listed on the US government's indictment for the 1998 bombings of the US embassies in Kenya and Tanzania, and he was sentenced to death in absentia by an Egyptian court a year later.
Zawahiri went into hiding after US-led and Afghan Northern Alliance forces toppled the Taliban in late 2001 for refusing to hand over bin Laden after the September 11 attacks.
In January 2006 Zawahiri escaped a US missile raid on a village in Pakistan's remote tribal areas that killed up to 18 other people.
In December 2001, reports said that his wife, son and two daughters had been killed in a US air raid on Kandahar, Afghanistan.
Pakistani journalist Hamid Mir, who met Zawahiri in 1998 and 2001, said he later remarried and his new wife gave birth to a baby girl in late 2005.