Osama bin Laden’s longtime deputy Ayman al-Zawahri has taken control of al-Qaeda, a widely anticipated move that comes at a time the terror network is struggling for relevance amid a wave of Arab uprisings that has threatened to upstage it.

Al-Zawahri, a surgeon by training, has long brought ideological fire as well as tactical and organisational cunning to al-Qaeda, which has found itself increasingly decentralised and prone to internal disputes following its expulsion from Afghanistan.

Al-Zawahri pledged to avenge the death of the al-Qaeda founder and mastermind of the 11 September terror attacks and to continue the terror network’s campaign of attacks against the US and other Western interests.

Al-Zawahri turns 60 on Sunday and has a $25 million bounty on his head, has been behind the use of suicide bombings and the independent militant cells that have become the network’s trademarks. But intelligence officials have said that some al-Qaeda members find al-Zawahri to be a controlling micromanager who lacks bin Laden’s appeal.

He also faces significant challenges in promoting al-Qaeda’s agenda of a religiously led state spanning the Muslim world after finding itself sidelined in the wake of popular revolts that have been driven by aspirations for Western-style democracy instead.

Al-Zawahri has been in hiding for nearly 10 years and is widely believed to be near the Pakistan-Afghanistan border. Many now predict that he would step up attacks to prove himself.

Al-Zawahri and bin Laden first crossed paths in the late 1980s in the caves of Afghanistan, where the Egyptian reportedly provided medical treatment to bin Laden and other Islamic fighters battling Soviet forces. Their alliance would develop years later into the 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.

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.

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 a tomb,” he said. He is right.