Four years ago, Michelle Obama told skeptical voters that despite her husband's funny name, he was just like them. On Tuesday, she tried to convince them he was also an exceptional president.

More popular than her husband, the First Lady kick-started the Democrats' 2012 convention with a prime-time address in Charlotte, North Carolina that marked another step on her path from reluctant campaigner to political heavy hitter.

While First Ladies since Nellie Taft 100 years ago have waded into the turbid waters of US presidential politics, Michelle reprised the modern role of providing a humanizing antidote to the hyper-partisan caricatures of the day.

It was before a stadium packed with supporters in Denver, Colorado four years ago that the Harvard and Princeton-trained lawyer made her political debut.

Then she sought to show Americans that the Obamas were indeed like them.

She also began to tell her own story -- that of a devoted mother and wife who made an improbable journey from the poor South Side of Chicago to the storied corridors of power in the White House.

She spoke touchingly of Obama playing basketball with her six foot six brother and of her now deceased father using two canes to get across the room to kiss her mother.

On Tuesday she made the case that he was also a compassionate and diligent president.

"When people ask me whether being in the White House has changed my husband, I can honestly say that when it comes to his character, and his convictions, and his heart, Barack Obama is still the same man I fell in love with all those years ago."

"That's the man I see in those quiet moments late at night, hunched over his desk, poring over the letters people have sent him.

"The letter from the father struggling to pay his bills, from the woman dying of cancer whose insurance company won't cover her care, from the young person with so much promise but so few opportunities.

"I see the concern in his eyes, and I hear the determination in his voice as he tells me, 'you won't believe what these folks are going through, Michelle. It's not right. We've got to keep working to fix this. We've got so much more to do.'"

In recent months, as the first black First Lady, with charm, hidden steel and growing political skill, she has injected some much-needed verve into her husband's battered brand.

She has headlined over 70 fundraisers since April, and in Charlotte has been drafted to not only headline the first night of the convention, but to lead a slew of side events to woo African American, Hispanic, gay, military and women activists.

Since occupying the East Wing of the White House she has also built goodwill with healthy eating and fitness campaigns, and a drive to help families of military veterans.

"She's the first fashionista, the mom-in-chief, the first gardener, the cool aunt -- she's Oprah with good arms," said Robert Watson, an expert on First Ladies from Lynn University in Boca Raton, Florida.

"I don't know if it's rebranding or we're finally getting the real Michelle. Whatever it is, it's very effective."

Born Michelle LaVaughn Robinson on January 17, 1964, she rose from a humble upbringing to go to two of the most prestigious US universities.

She worked in corporate law, as director of a community non-profit in some of Chicago's less moneyed neighborhoods, and at the University of Chicago and its medical center.

But she has not been without detractors.

In the 2008 campaign an affectionate tap of clenched fists with her husband was dubbed 'a terrorist fist jab' and she was called 'unpatriotic' for an unguarded comment in which she said the public support for her husband made her proud of her country 'for the first time in my adult lifetime'.

A lavish trip to Spain in 2010 was panned by critics and mocked by conservative radio talk show hosts as evidence of undue entitlement.