Eighteen years ago, she was accused of hurting her husband’s campaign for the U.S. Senate in Massachusetts.

Four years ago, after Mitt Romney’s failed bid for the Republican presidential nomination, she begged him not to run again.

But today, Ann Romney is considered one of her husband’s biggest politics assets, helping soften the sometimes rigid demeanor he portrays as he runs for president.

Tuesday, she will deliver one of the most important speeches of the Republican National Convention, a potentially pivotal moment meant to help voters see her husband as she does and perhaps overcome one of the main challenges of his candidacy. Her remarks are considered so important to her husband’s prospects that the campaign shuffled the calendar to make sure her address would be televised on the broadcast networks.

The homemaker – a 63-year-old grandmother of 19 known as “Mamie,” who beat breast cancer but is still afflicted with the debilitating disease of multiple sclerosis – has managed to connect with voters in a way her husband of more than four decades has not. She’s been a constant on the campaign trail for months, her presence relaxing him while she’s also appearing in ads, political events and in interviews. She’s even a much sought after fundraising draw.

“I’m sold already,” said Tony Jackson, 49, a convention delegate from Florida. “She’ll make a great first lady.”

Republican former Mississippi Gov. Haley Barbour said she will play a critical role in defining her husband because Americans don’t know much about him, and what they have been told is not always flattering or true – he’s wealthy, he doesn’t care about everyday people, he shipped jobs overseas.

“I think it’s important for the spouse of any candidate because nobody knows them better. Nobody knows little things about Mitt Romney,” Barbour said. “The purpose of this convention is for the American people to see who Mitt Romney really is and what he’s really done.”

Romney, speaking to reporters Monday in New Hampshire, spoke briefly of his wife’s role on Tuesday. “I like my speech. I really like Ann’s speech,” he said. “She’s going to do terrific.”

Ann Romney declined to comment for this story. Her spokeswoman said Monday that her speech was still being finalized but that she planned to talk about the couple’s relationship and his role as husband and father. “Mrs. Romney is excited to have the opportunity to share her heart with millions of Americans,” Sarah Haley said.

“The country does vote for the candidate it likes,” said Lee Miringoff, director of the Marist Institute for Public Opinion, which conducts the McClatchy-Marist poll. “The likability numbers have gotten better for him, but he still needs to improve. He just doesn’t connect that way.”

A fellow native of Michigan, Ann Lois Davies started dating Romney in high school when she was 16. Young Mitt, the son of Michigan Gov. George W. Romney, caught her eye at a party.

The two got engaged at the senior prom and her 1967 yearbook took a guess at what was to come, printing the words “first lady” next to her photo. They were married two years later at a ceremony attended by the presidents of Ford Motor Co. and General Motors Corp. and Rep. Gerald R. Ford. She made the decision to convert to Mormonism, her future husband’s religion.