The assassination of Sheikh Ahmed Yassin could be a watershed event - for the Middle East as a whole perhaps, but certainly for Hamas, the militant organisation that he founded.
By Martin Asser
BBC News Online
Yassin helped found Hamas in 1987 and he masterminded the development of its potent blend of religious dogma, armed struggle, martyrdom and social welfare.
Sheikh Yassin was seen as more than just Hamas leader
Over the years, he stood above the factional differences between Hamas' pragmatic and radical strands, and between its local and exiled leadership.
So his death leaves a massive gap - to paraphrase Israel's view, the "snake" has indeed been decapitated.
But many observers are asking whether the snake will turn out to be a hydra of Greek mythology, thwarting its opponents by sprouting ever more dangerous and vindictive successor-heads?
Some say that Sheikh Yassin is just as important to Hamas dead as he was alive, if not more so. The propaganda value of what is seen as his martyrdom, and the imagery of a modern missile killing a man in a wheelchair, may serve as to recruit Hamas followers.
But that does not take into account the hugely effective political game that this frail figure has played.
"There's no doubt he was a very important symbol," says Dr Magnus Ranstorp, a terrorism expert at St Andrews University.
"He was the only person who was able to unify the different strands of Hamas, in the West Bank and Gaza, and abroad, and there is no obvious person who can fill his shoes," he told BBC News Online.
Sheikh Yassin was routinely called Hamas' spiritual leader by observers (a title the Israelis have taken issue with, calling it an "insult" to religion because he endorsed what they see as terrorism).
But to supporters he was the Hamas leader, pure and simple; the qaid [leader], or the sheikh.
With Hamas' system of separate organisations operating in parallel - the military wing, the multi-faction political sphere, the charitable works - Ahmed Yassin was the overarching authority over all of these - not the operational head of any one part of the organisation.
Monday's assassination means Hamas will struggle to find a leader of similar stature.
In the immediate aftermath, a triumvirate of politburo members - Abdel-Aziz Rantissi, Mahmoud Zahhar, and Ismail Haniya - are coming forward to fill the void.
Mr Rantissi - a hardline opponent of ceasefires with Israel - is seen by many as the most powerful of these, a "first among equals". Mr Rantissi has now been appointed Hamas leader in Gaza.
Rantissi is a hardline figure in Hamas
But Hamas-watchers in Gaza say he is ill-equipped to take on the mantle of the sheikh - who was in many ways a pragmatic figure, able to bend with prevailing opinion as well as bind together Hamas' disparate strands.
Khaled Meshaal, a Hamas leader based in Damascus, is now the groups main overall head.
Twists and turns
In the short term, there will undoubtedly be an upsurge of attacks by Hamas against Israeli targets - in all likelihood civilians. That is something supporters and critics of the assassination can agree upon.
But things may take other less predictable turns.
The Palestinian Authority could lose even more ground to Hamas, and its failing security apparatus will be even less able to prevent suicide bombings and other militant attacks.
The Palestinian street, meanwhile, is united in its revulsion at the killing of a man seen overwhelmingly as an Islamic leader, the only one of any note in Palestinian politics.
And who knows what other targets Hamas may choose in its quest to swap blood for blood? Sheikh Yassin, by all accounts, put the brakes on operations beyond Israel's borders. Those brakes may come off.
And reporters on the ground say there is an appetite among lower echelons for retribution against the US, which supplied the military hardware and which singularly declined to condemn the assassination.
Long term plans
Critics of Israel - and there are many on the killing of Sheikh Yassin - say there is much to fear from what is seen as a reckless, provocative act. But Dr Ranstorp says things may prove easier in long run - for both Israel and the PA.
"Israel has long experience in how to deal with Hamas. It knows how to counterbalance the various factions and where to apply pressure - after all it has the addresses of every single Hamas leader, and it knows where to find them," he says.
It is the foot soldiers of Hamas, he argues, that Israel has difficulty dealing with - including the young people who blow up buses and kill civilians.
"That is why Prime Minister Ariel Sharon is pressing ahead with the unilateral separation plan - which is why he played the card of killing Yassin now, when he needs it."
But Hamas thrives on conflict, and Dr Ranstorp acknowledges that it is remarkably steadfast in pursuit of its own long-term strategic objectives.
"Every time I met Yassin and other senior Hamas figures, they were consistent about one thing.
"They will create a Palestinian state by 2022 or 2023, with demography and Islamic revolution in Jordan and so on - everything else for Hamas is just tactical manoeuvring".