Nkosazana Dlamini-Zuma: What next for African Union boss?

As Nkosazana Dlamini-Zuma steps down as the head of the African Union Commission, will she take over from her ex-husband as president of South Africa?

For two decades Ms Dlamini-Zuma has been the quiet juggernaut of South African politics. Tough, highly educated, competent, aloof, and most importantly, rarely out of a job.

The 67-year-old medical doctor has served in the cabinets of all four of South Africa's post-apartheid presidents - demonstrating an instinct for political survival and a capacity for endurance shared by few of her colleagues. Since 1994 she has been minister of health, foreign affairs and home affairs.

But now comes what may be Ms Dlamini-Zuma's defining challenge.

After four years away from South Africa's fractious political battles, as chairperson of the African Union Commission in Addis Ababa, she is poised to return home to run for the leadership of the governing ANC this December - a job that could, in turn, catapult her to the country's presidency in the 2019 national elections.

Zuma's protector?

Her supporters insist she's the perfect fit - a steady, hugely experienced, glass-ceiling-smashing woman, ideally positioned to reunite and reconcile the ANC's increasingly divided factions and to give the party a new lease of life to counter its steady slide in recent polls.

Her absence from South Africa during the past few years is seen as another, perhaps deliberately-planned, advantage - leaving her untainted by the scandals and power struggles that have damaged other prominent figures now challenging her for the top job.

Who is Nkosazana Dlamini-Zuma?

• Anti-apartheid activist

• Fled South Africa and completed her medical training in UK

• Met her ex-husband, current President Jacob Zuma, while she was a doctor in Swaziland

• After 16 years, divorced Mr Zuma in 1998

• Declined the offer of replacing her sacked ex-husband as deputy president in 2007

• Chair of the African Union commission 2012 - 2016

But her critics find plenty to object to in that portrait.

For a start, they point to her time at the African Union, which began with a notably divisive election campaign.

To some observers, Ms Dlamini-Zuma went on to become a lacklustre chairperson, only half committed to the job, and too easily distracted by grand projects rather than setting the agenda and leading the responses to the continent's most urgent crises - from the Ebola outbreak to the conflicts in South Sudan, Mali, Somalia and beyond.

Mr Zuma publicly congratulated his ex-wife after she was sworn in as the head of the African Union Commission

Her supporters hit back by saying she has taken a more long-term, developmental approach to problem solving, which may have generated fewer headlines, but served the continent better.

Then there is the profoundly complex issue all too neatly summed up by the second half of her surname, Dlamini-Zuma.

From 1982 to 1998 she was married to South Africa's current president, Jacob Zuma. The couple raised four children before getting divorced.

Since then, their political relationship has appeared to shift, with Ms Dlamini-Zuma at times seeming to back her former husband, and at other times overtly siding against him.

The suspicion, now openly articulated by President Zuma's opponents, is that the current South African leader is actively promoting his ex-wife's bid to replace him, in the belief that as president, she will be able and willing to protect him from what he sees as a range of politically-motivated legal challenges and corruption investigations that could well pursue him after he leaves office.

Only recently, Mr Zuma added fuel to such speculation by appearing to weigh in on the succession debate by saying the ANC was "ready" to be led by a woman, rather than backing his current deputy president Cyril Ramaphosa.

To many, this line of attack against Ms Dlamini-Zuma is little more than a cheap sexist slur against a formidable and independent politician.

The Clinton effect?

And yet the perception of family bias clearly exists and, more to the point, in a no-holds-barred contest, it will almost certainly be wielded relentlessly in order to damage her chances of being elected ANC leader.

Some draw parallels with Bill and Hilary Clinton in the US, and the sense that South African voters may simply have grown tired of the Zuma name and any hint of a political dynasty.

The comparison is unfair, given that the Zumas are long divorced.

But there is no doubt that Jacob Zuma - his presidency increasingly overshadowed by scandal - has become an electoral liability for the ANC, and that Ms Dlamini-Zuma will have to position herself as something other than a continuity candidate if she is not only to win December's vote, but to convince South Africans that after nearly a quarter of a century in power, the ANC still deserves to remain in power come 2019.