How will Zawahiri transform al-Qaeda?
The reported rise of Ayman al-Zawahiri to al-Qaeda's helm is seen by Pakistani experts as unlikely to cause drastic changes in the security situation in Pakistan or around the world.
But opinions differ on the potential of the Egyptian doctor to control disparate Islamist groups and translate their influence within some state institutions in Pakistan and elsewhere to fuel wider discontent in the Islamic world.
"Zawahiri has become the effective leader of an organisation of which he was already the de-facto operational head for several years," says Zahid Hussain, a senior journalist and author of book Frontline Pakistan: The Struggle With Militant Islam.
"So, not much is likely to change."
Experts believe Zawahiri brings with him varied experience of civil, political and military matters.
- Born in Cairo, Egypt, in 1951
- Trained as an eye surgeon
- Helped found the Egyptian Islamic Jihad militant group
- Known as Osama Bin Laden's right-hand man and the chief ideologue of al-Qaeda
- "Operational brains" behind the 9/11 attacks
- $25m (£15m) bounty on his head
Journalist and analyst, Rahimullah Yusufzai, who has met Zawahiri twice, describes him as a "well-read, knowledgeable" man who has delved into politics, was a prisoner, worked as a medical aid worker, became a guerrilla fighter, organised funding, recruitment and deployment of al-Qaeda fighters, emerged as a propagandist and ideologue, and finally became a militant leader.
But he also carries the burden of fractious Egyptian politics, reflected in the thinking of disparate Egyptian groups within al-Qaeda that will pose a challenge to his unifying skills.
A greater challenge - and one that is of major concern in the West - would be to increase al-Qaeda's inputs into the planning and guidance of worldwide attacks against Western interests to the level it displayed at the turn of the millennium.
Breath of fresh air?
Mr Yusufzai says Zawahiri does not match Bin Laden's stature and charisma as a "princely" warrior who brought personal wealth to his cause and could command respect of all Islamist groups, whether within the al-Qaeda fold or beyond it.
But even Bin Laden was far from controlling the organisation towards the end of his days. Every group was on its own, he says.
The fact that it took al-Qaeda nearly six weeks to announce Bin Laden's successor points to continuing disarray in organisation's ranks, says Mr Yusufzai.
"It shows that they have operational difficulties, and problems with logistics and security," he said. "They are on the run, and are trying hard to survive."
But some believe Zawahiri does bring a breath of fresh air to al-Qaeda and its affiliates.
"Unlike Bin Laden, who had for several years become confined to that compound in Abbottabad, Zawahiri has remained mobile, and has been regularly putting out video and audio messages to mobilise opinion in the Muslim world," says Zahid Hussain.
Zawahiri was last sighted in Afghanistan's Khost province, close to Pakistan's North Waziristan tribal region, in October 2001, days before the Americans stormed and dislodged the Taliban regime in Afghanistan.
In early 2006, he escaped a drone strike on his hideout some 300km to the north, in Pakistan's Bajaur tribal region.
Since then, there have been several unconfirmed reports of his presence in the Bajaur border region as well as in some Pakistani cities, including Abbottabad, where Bin Laden was found and killed by Americans on 2 May.
Zahid Hussain says that while al-Qaeda never exercised centralised control over its affiliated groups, in recent years it has attracted a lot of recruits in Pakistan while some armed groups in Libya, Yemen and Somalia have drifted close to it.
"There is an ideological fusion between al-Qaeda and these groups, and there is also potential for loose co-operation."
He says many in the Pakistani security establishment believe Zawahiri is the motivating figure behind the recent upsurge in militant attacks in Pakistan.
Some of these attacks - such as the one on PNS Mehran in May or the November 2010 attack on CID building in Karachi - have exposed the disturbing reality that militants linked to al-Qaeda have penetrated deep into the Pakistani armed forces.
In from the cold?
The extent of this penetration is not known, and therefore it is hard to assess their capacity to hold Pakistan's military leadership hostage to their strategic aims.
But some in Pakistan believe there is considerable fear within the military top brass of an "implosion" in its ranks if a vigorous anti-militancy strategy is pursued.
As he turns 60 this month, Zawahiri will be hard-pressed to do something different, something that can bring al-Qaeda in from the cold.
His best bet would be the Pakistani militant groups who at the moment offer the sole guarantee for al-Qaeda's survival.
His challenge would be to knit these groups into a unified force that can destabilise Pakistan, an ally of the "Crusaders and Jews".
Secondly, he would like to find ways to make al-Qaeda more relevant to ongoing popular insurgencies in the Arab world, few of which draw their inspiration from militant Islam.
And, if luck were on his side, he would like to launch a spectacular attack somewhere in the West on the pattern of 9/11 or 7/7.
Much of what he can or cannot achieve will become apparent with time, but for the moment few are willing to bet against him.