Following Mitt Romney on the campaign trail for a few days only confirms his reputation as slightly wooden -- so it's a good thing his wife Ann is there to humanize him, if only a little.

The 62-year-old, who regularly appears on the podium with her husband and their five smartly-dressed sons, tells a joke aboutRomney's failed 2008 White House bid and his decision to run again.

"I will tell you that four years ago, I was definite about one thing: I would never do this again," she told the audience, introducing him at one of the candidate's recent two- or three-a-day campaign stops.

"And I can't even tell you how much I really meant that. And Mitt laughed, and said: 'You say that after every pregnancy'," added Romney, whose husband has cemented his position as Republican presidential frontrunner this week.

Their visibly squeaky-clean and loving family life -- which the Mormon businessman-turned-politician's camp likes to contrast with the three marriages of his main Republican rival Newt Gingrich-- is a clear vote-winner.

They routinely call each other "sweetie" and hold each other's hands. He regularly refers to her as "the boss," and her warm introductions and banter contrast with Callista Gingrich's fixed smile at her husband's side.

"You can see she keeps him grounded," said Greg Hampton, among a huge crowd in a school sports hall in Colorado this week, ahead of Tuesday's caucuses here and in Minnesota, and a primary vote in Missouri.

But while the 64-year-old former Massachusetts governor appears well on course to win his party's nomination to take on President Barack Obama in November, it has not always been so rosy.

His wife was diagnosed with multiple sclerosis in 1998, and although she brought it under control with a combination of orthodox medical and other means -- including horse riding -- she more recently battled breast cancer.

"She credits her husband’s unwavering care and devotion to her for helping her through these ordeals," Romney's campaign website says, describing the dark years.

The couple met in elementary school, when Mitt "remembers tossing pebbles at her when she rode by on a horse. When they met again years later at a friend’s house, he was smitten," it says.

They both went to Brigham Young University in Utah, and she converted to his faith as a member of the Church of Jesus Christ of Latter Day Saints (LDS). She later completed her studies at Harvard after they had children.

Ann Davies and Mitt Romney married in 1969 after he returned from two years' missionary work in France, and as well as five sons have sixteen grandchildren, "who are the center of their lives." They have been married for 43 years.

That may seem a politically rose-tinted account, but over the course of two relentless White House primary campaigns, no one has found any significant dirt on them.

Again, that contrasts with Gingrich's messy personal life. Last month his second wife accused him of having asked for an "open marriage" while having an affair with Callista, who later became his third wife.

"It seems to be a very good marriage, and it's Romney's only marriage. In this day and age that's saying something!" said Harvard expert Elaine Kamarck, author of a book on US primary politics.

So what for the future? Ann Romney, who has done significant charity work, including as Massachusetts First Lady from 2003-2007, has said little about what she would do if she and her husband end up moving into the White House.

She may not be a top-flight attorney like Michelle Obama, but Romney claims his wife could bring her experience -- and her less buttoned-down, more visibly caring personality -- to Washington, DC.

"She is a real champion and a fighter," he said when asked what skills his wife could bring to the role of First Lady during a televised debate in Florida last month.

Recalling her multiple sclerosis and 2008 breast cancer scare, he said: "She has battled both successfully.

"And as First Lady, she will be able to reach out to people who are also struggling and suffering and will be someone who shows compassion and care," he said.

John Brehm, politics professor at the University of Chicago, said her impact on her husband's popularity was unclear.

"I haven't seen any polling data which shows any effect -- positive or negative -- towards her. People generally like Michelle Obama, quite a bit more than they like President Obama," he said.

"But no one votes for presidents' wives, or husbands, should that ever become a reality," he added.