Al-Zawahiri: Al-Qaeda chief overshadowed by Bin Laden
Ayman al-Zawahiri was the long-time second-in-command to Osama Bin Laden.
A doctor from a prominent Egyptian family, he has been known for his organisational skills rather than for his inspirational qualities.
In jihadist circles he has neither the charisma nor the dynamic "back-story" of his predecessor, but nonetheless he remains a respected figure.
In one sense then he represents the face of continuity within al-Qaeda. However, it is unlikely to be business as usual for the organisation under his leadership.
For one thing he is not Osama Bin Laden.
He takes charge of "the brand" at a time when it has suffered some serious reverses in addition to the killing of its long-time leader.
The death of Fazul Abdullah Mohammed - a key al-Qaeda player in East Africa - is just one example. He was the mastermind of the US embassy bombings in Kenya and Tanzania, and was shot at a road-block in Somalia less than a week ago.
Many analysts wonder if al-Zawahiri has the personal qualities to lead an organisation that now resembles more a collection of franchises - a conglomerate of regional affiliates - than a single centralised body.
The internal workings of al-Qaeda still remain hard to penetrate.
Analysis of material at Bin Laden's hide-out in Pakistan suggests to some experts that he was much more than just a figurehead - that he actually had far more to do with operational matters than many had previously imagined.
The delay in the announcement of al-Zawahiri's appointment has also prompted comment.
Time has passed since the death of Osama Bin Laden. Analysts have been speculating about the reasons for this apparent delay.
Is this a sign of internal problems and differences, or is it simply an indication of the complexity of decision-making in an organisation distributed over a wide area, whose senior figures are under constant threat of attack?
But perhaps the most significant problem facing al-Zawahiri is that the wider context in which al-Qaeda operates has changed dramatically.
What has been dubbed the "Arab Spring" has sent shockwaves around the Middle East as rulers have been toppled in Egypt and Tunisia.
It has been the popular desire for democracy that has been the agent of change, not the Islamist violence advocated by al-Qaeda.
Ayman al-Zawahiri has sought to link al-Qaeda with this process of change with little apparent success.
Indeed, attitudes in much of the Arab world towards al-Qaeda had been shifting long before the Arab Spring, prompted not least by the terrible violence against fellow Muslims perpetrated by jihadist elements in Iraq.
The Arab Spring, at least for now, suggests that al-Qaeda's message is in large part redundant and irrelevant to the masses of ordinary people who desire change.
Al-Zawahiri's call for Egypt to become an Islamic caliphate seems out of tune with the actual sentiments on the ground.
There is, though, another aspect to the Arab Spring. For all the continuing aspirations for change, the track record so far has been mixed - repression in Bahrain, even more so in Syria, some progress in Tunisia and Egypt. But even there the march to democracy seems to have faltered.
Some experts fear that if hopes for peaceful change in the region are dashed, then al-Qaeda's message may again gain traction.
Indeed, Yemen could well be the critical country in al-Qaeda's immediate future.
Upheavals there have brought the near collapse of the ruling order. The economy is on its last legs.
Yemen is home to one of the organisation's most important regional off-shoots - al-Qaeda in the Arabian Peninsula (AQAP).
Its operational centre of gravity seems to have moved there. In Yemen there is a new generation of younger, radical leaders like Anwar al-Awlaki - the target of a recent failed US drone strike - who are playing an increasingly prominent role in al-Qaeda's decision-making.
How Ayman al-Zawahiri copes with all these challenges, along with the continuing efforts of the US and its allies to disrupt his organisation, will determine whether al-Qaeda has a future.
But what is not in doubt is al-Zawahiri's implacable hostility to the United States and the West, and his desire to exact revenge for Osama Bin Laden's death.