The controversial Internet Corporation for Assigned Names and Numbers (ICANN) has weathered violent political turbulence and volatile technical controversies since its founding in 1998.

But in a few months the non profit organisation may face one of its toughest challenges when long time chairman Vint Cerf steps down.

A board member since 1999 and chairman since 2000, Cerf has been instrumental in helping ICANN through thorny crises and painful evolution. He will give up his seat on the board in October to comply with ICANN term limit policies.

All along, despite flaws and missteps, ICANN has fulfilled its core duty of overseeing the internet's address system and ensuring its overall security and stability.

Assessments of Cerf’s tenure vary but the consensus is that while far from perfect, he has been a very effective chairman who has steered ICANN skillfully during the crucial early years.

"Vint is incredibly knowledgeable and thoughtful and he lent a great deal of credibility and experience to the ICANN board," said David McGuire, communications director at the Centre for Democracy and Technology, a US non profit think tank for internet public policy issues.

Despite the recurrent criticisms that ICANN responds disproportionately to US government interests, Cerf is credited for patiently building consensus and creating a collegial, collaborative atmosphere among the group's different constituencies.

Mark Uncapher, senior VP and counsel at US industry body the Information Technology Association of America, said: "He has done a superb job. Although Vint is best known for his technical contributions, he also has considerable political skills."

If instead of Cerf, ICANN had an impatient chairman who routinely short circuited the group's collaborative decision making process, the internet might have been in very bad shape today, he added. "That might have led to the ultimate threat: the ‘balkanisation’ of the internet, where countries go in different directions and there isn't a single point of contact the way there is with ICANN."

In addition to being generally considered a strong, reasonable and sensible leader, Cerf also brought his reputation to the ICANN board. Considered one of the fathers of the internet for his work in creating its basic architecture, Cerf is respected and admired worldwide, having received many awards and recognitions.

This standing as a legitimate internet luminary has allowed Cerf to intervene and prevent acrimonious disagreements within ICANN from escalating into war like confrontations, experts say.

However, having a living legend as board chairman has also had negative effects, according to Oscar Robles-Garay, general manager at Mexico's internet NIC (network information centre) for the .mx domain: "His strong leadership is his best quality but it has also backfired on him, as some board members have at times felt strongly influenced to vote the same way as Vint, even when he was wrong."

Milton Mueller, professor of information studies at Syracuse University in New York, faulted Cerf for "a very conservative and limiting approach to ICANN policies." But he said the chairman nevertheless gave ICANN stability and cohesiveness, adding: "He has been in general willing to go along with US control and hasn't been a big advocate for internationalising ICANN."

For Ian Peter, senior partner at consultancy Ian Peter & Associates and founder of the internet Mark 2 Project in Australia, Cerf excelled in giving broad credibility to a young organisation and guiding it through its critical growth phases.

However, Peter admitted that Cerf lacks strong corporate management skills and has let bureaucracy grow "massively". He said that Cerf also leaves unresolved the issue of the US government's ICANN oversight. The internet Mark 2 Project analyses issues affecting internet governance.

This issue dates back to ICANN's formation as an international organisation that could progressively absorb internet management functions until then handled by the US government. The process to give ICANN full autonomy hasn't been completed yet, despite the belief of many that it's overdue.

Cerf's successor will have a full plate of ongoing policy and technical issues that are in various stages of discussion, testing and implementation.

Those include generic top level domains, international domain names and the organisation's attempts to become more accountable and transparent. Other efforts are a significant revision of the process for accrediting registrars and the implementation of digital signatures to help authenticate matches between domain names and internet addresses.

ICANN experts interviewed generally agreed on some key skills and traits that Cerf's successor needs to have, such as a strong technical knowledge of internet architecture issues; and an ability to build consensus by being approachable and open to diverse ideas. And a willingness to work for no pay, because ICANN's chairmanship is pro bono work.

"I don't think there's anybody in the ICANN community who is looking for 'Vint Two' because there isn't one," said Paul Twomey, ICANN's CEO, during a press conference at the closing of the group's 29th International Public Meeting in Puerto Rico. "The board is very concerned about this issue."

The board will elect Cerf's successor at its next International Public Meeting in Los Angeles, which starts on 29 October and ends on 2 November. Making a good choice will be key to the future of this extremely important organisation.

Twomey added: "There's nobody saying ‘X is the answer’ and everyone agreeing. There is lot of discussion and the board is prepared for a decision on it."

After eight years of being heavily involved with ICANN, Cerf will not have to be dragged kicking and screaming from his board seat. When he bids goodbye to the board in October, he plans to distance himself from the organisation for at least one year. Cerf, who is 64 years old, will make himself available for consultations but will not take on any formal duties.

One reason is that he wants to devote more time to other activities including, as he describes it, his "day job" as Google's chief internet evangelist. "I've given a good chunk of my time to ICANN already," Cerf told IDG News Service this week. "To be quite honest, eight years is a long time. I'm not sure I'd stand for re election to the ICANN board.”

Cerf believed that leaving the post would be good for his successor and the board members as they establish their way of working together. "I don't want to be a hovering shadow," he said.

It seems that come October, Cerf’s era at ICANN will end, and the organisation will have to take on the challenge of learning to live without him.