Al-Qa'ida's long-time second in command, a doctor from a prominent Egyptian family, has succeeded Osama bin Laden as head of the terror group, it said today.
Bin Laden was killed in a US special forces raid on his Pakistan hideout last month.
Ayman al-Zawahri, who turns 60 on Sunday, has long brought ideological fire, tactics and organisational skills to al-Qa'ida.
The surgeon by training has promoted the use of suicide bombings and independent terror cells that have become the network's trademarks.
He is believed to be living somewhere near the Pakistan-Afghanistan border and has appeared in dozens of videos and audiotapes in recent years, increasingly becoming the face of al-Qa'ida as bin Laden kept a lower profile.
The two terror leaders first crossed paths in the late 1980s in the caves of Afghanistan, where al-Zawahri reportedly provided medical treatment to bin Laden and other Islamic fighters battling Soviet forces.
Their alliance would develop years later into the al-Qa'ida terror network blamed for America's worst terror attack in its history.
In a videotaped eulogy released earlier this month, al-Zawahri warned that America still faces an international community of Muslims that seek to destroy it.
"Today, praise God, America is not facing an individual, a group or a faction," he said, wearing a white robe and turban with an assault rifle leaned on a wall behind him. "It is facing a nation that is in revolt, having risen from its lethargy to a renaissance of jihad."
Al-Zawahri also heaped praise on bin Laden and criticised the US for burying him at sea.
"He went to his God as a martyr, the man who terrified America while alive and terrifies it in death, so much so that they trembled at the idea of his having tomb," he said.
In a website statement, al-Qa'ida gave no details about the selection process for bin Laden's successor but said that it was the best tribute to the memory of its "martyrs".
Al-Zawahri is the son of an upper middle class Egyptian family of doctors and scholars. His father was a pharmacology professor at Cairo University's medical school and his grandfather was the grand imam of Al-Azhar University, a premier centre of religious study.
At the age of 15, he founded his first underground cell of high school students to oppose the Egyptian government. He continued his militant activities while earning his medical degree, later merging his cell with other militants to form Islamic Jihad.
Al-Zawahri later served three years in an Egyptian prison before returning to Afghanistan in 1984 to fight the Soviets, where he linked up with bin Laden. Al-Zawahri later followed bin Laden to Sudan and then back to Afghanistan, where they found a safe haven under the radical Taliban regime.
Soon after came the 1998 bombings of the US embassies in Africa, followed by the 2000 suicide bombing of the USS Cole off the coast of Yemen, an attack al-Zawahri is believed to have helped organise.
In a 2001 treatise, he set down the longterm strategy for the jihadi movement - to inflict "as many casualties as possible" on the Americans.
"Pursuing the Americans and Jews is not an impossible task," he wrote. "Killing them is not impossible, whether by a bullet, a knife stab, a bomb or a strike with an iron bar."
Al-Zawahri's hatred for Americans has also become deeply personal: His wife and at least two of their six children were killed in a US airstrike following the 2001 US invasion of Afghanistan after the 9-11 attacks.
He has worked in the years since to rebuild the organisation's leadership in the Afghan-Pakistan border.
Al-Qa'ida has inspired or had a direct hand in attacks in North Africa, Saudi Arabia, Yemen, Pakistan, the 2004 train bombings in Madrid and the 2005 tube and bus bombings in London.
The statement announcing his succession was filled with the terror network's usual rhetoric, vowing to continue the fight against what it called "conquering infidels, led by America and its stooge Israel, who attack the homes of Islam".
The al-Qa'ida statement also stated the group's support for this year's popular uprisings in Egypt, Tunisia, Yemen, Syria and Libya.
"We encourage the people of Islam to rise up and continue the struggle, persistence and devotion until all the corrupt and oppressive regimes imposed by the West are gone," it said.