New York (AFP) - Former president Bill Clinton celebrates his 70th birthday Friday poised to make history as America's inaugural "first gentleman" should his wife win the election and propel the couple back into the White House, roles reversed.

It remains unclear what role or what influence Clinton, the US president from 1993 to 2001, would have in this still undefined role — generally dubbed "first gentleman" but also occasionally "first mate," "first man" or even "first dude."

As elder statesman and orator without equal, he occupies a unique place in US politics. Popular at home and active overseas thanks to his Clinton Foundation, he has given little away about a possible White House career, take two.

Instead he has merely joked that he would like to "break the stranglehold that women have had on the job of presidential spouse."

White haired, with one of the most distinctive voices in the world and vegan since 2010 after suffering health problems, Clinton has campaigned tirelessly on his wife's behalf for months.

If he caused controversy when Hillary Clinton was campaigning against Barack Obama in 2008 with sometimes ill-chosen words and being too visible, this time he has kept a lower profile — content to reel off anecdotes, make pleasantries and attack her Republican rival Donald Trump at hundreds of campaign stops.

He is more discreet, his wife's campaign only too aware that his infidelities and their marital strife are damaging baggage, which Trump has repeatedly tried to exploit.

At the Democratic convention last month, he confined his speech to humanizing his wife, talking about the fellow student with whom he fell in love.

What is certain is that Bill Clinton is too flawed and too political to pick out the china and play stay-at-home spouse back in the White House.

During a campaign stop in Kentucky, Hillary Clinton said in May that she would put Bill "in charge of revitalizing the economy, because, you know, he knows how to do it," especially "in places like coal country and inner cities."

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The Clinton years stand out for their balanced budgets and economic growth, when millions of jobs were created. But Hillary Clinton has made it clear she does not intend to offer him a cabinet job.

- Presidential cookies -

First ladies, who have their own staff and office, traditionally confine themselves to worthy areas of influence, such as reading and education for Laura Bush, or gardening, healthy eating and military veterans for Michelle Obama.

Will Bill settle on a cause like these? How will the most powerful political couple of their generation coexist in the White House?

"He'll be given some kind of big visible role in some policy areas, but nothing that would overshadow in any way the president," says Robert Shapiro, professor of political science at Columbia University in New York.

"Also, I imagine behind closed doors, he will be giving her advice," Shapiro added.

Bill Clinton, who at 70 will be the oldest spouse to enter the White House, appears to be preparing himself.

For months. he has no longer delivered paid speeches, according to NBC News. These speeches earned him millions of dollars in 2015.

He also plans to stop raising money for the Clinton Foundation and turn its running over to independents if his wife wins, says The Wall Street Journal.

And he bowed to a tradition for spouses of White House candidates, submitting along with Melania Trump a favorite cookie recipe to Family Circle magazine ahead of a readers vote on which one is best.

Not particularly motivated, he simply handed in the same oatmeal chocolate chip recipe that Hillary submitted in 1992 and 1996, redubbed a Clinton family favorite.

Oddly enough the cookie vote was born out of controversy sparked by Hillary during her husband's first run in 1992 in talking about her desire to pursue her own career.

"I suppose I could have stayed home and baked cookies and had teas, but what I decided to do was to fulfill my profession, which I entered before my husband was in public life," she said at the time.

The remark was interpreted as a criticism of stay-at-home moms and gave birth to the idea of readers voting on the presidential cookies. It was a contest that Hillary Clinton won both in 1992 and 1996.