She stands less than 5 feet tall and counts humor as her secret weapon. Today, she makes history.

Sen. Barbara Mikulski, a 74-year old Maryland Democrat, likes to say how unlikely it is that someone like her would ever come to the U.S. Senate. But today, as the 112th Congress convenes, she becomes the longest-serving female senator in U.S. history.

"I never thought of myself as a historical figure. But when the Library of Congress called and said, 'You're going to break the Margaret Chase Smith record, and we want historical artifacts,' I was taken aback," Mikulski told ABC News' Diane Sawyer. "To me, history is powder wigs and Jane Addams and Abigail Adams. Both pioneers in their own right.

"I think, for me, it's not how long I've served, it's how well I've served."

Tune in to 'World News With Diane Sawyer' Friday at 6:30 p.m. ET to watch Barbara Mikulski honored as our 'Person of the Week'

And with the new Congress, coming off contentious midterm elections that saw her party get thrashed at the polls, Mikulski said Republicans and Democrats need to work at civility.

"I think it's going to be full of challenges. We're going to want to stop bad things from happening," she said.

"We'll fight the repeal of Obama health care. We don't want to privatize Social Security," she said. "But we've got to work for a strong economy. And this is why I'd like to get back to that strong feeling of bipartisanship."

Mikulski said she already "kind of surveyed the women" after the election to get to know them and to build a consensus on certain issues.

"Even where we disagree, we don't have to be disagreeable. We're not a caucus. We disagree on issues like pro-choice, where to cut the budget," she said. "But we are a force," often on such issues as women's health care.

Mikulski, the daughter of a Baltimore grocer, said that when she was growing up, politics was a world away.

"Old guys who smoked cigars with potbellies, and they were named Tom, Dick and Harry," she said. "Now politicians are named Barb, Bev and Hillary."

But Mikulski secured a seat on the Baltimore City Council in the early 1970s, followed by a seat in the U.S. House of Representatives a few years later.

She described her best day in Congress as the day she stood on the Senate floor and fought for preventive health care for women, an amendment that later passed.

Her worst day, she said, was Sept. 11, 2001, when she and the rest of Congress were forced to run from what they feared would be an attack on the Capitol building.

"I'm a little on the chunky side, but I tell you I ran all the way and over to the Supreme Court and didn't break a sweat," she said. "It was a terrible day.

"But that day when we stood on the Capitol steps and bipartisans sang 'God Bless America,' I would never want to go back to that day. But I would like to go back to that feeling of togetherness."

Another First for History-Making Senator Barbara Mikulski

Although Mikulski makes history today, for her it's just another marker in a long line of firsts.

She was the first Democratic woman elected to the Senate, the first Democratic woman to serve in both houses of Congress, the first Democratic woman senator elected to a leadership post, the first woman elected to statewide office in Maryland -- and the list goes on.

Lest anyone think that Mikulski's tenure on Capitol Hill has been only about milestones, it has also been one of historic legislative accomplishments.

She fought hard for passage of the Lilly Ledbetter Fair Pay Act, a bill to guarantee equal payment for women, and railed against President George W. Bush in April 2008 when he threatened to veto the measure.

"But now the president has issued a veto threat. He said this bill is going to 'impede justice.' That is baloney," she said. "This bill doesn't impede justice, it restores justice. It reinstates a fair rule for both workers and employers. He said it is going to mess up the process. This bill does not slow down the process. It gives people a way of getting into the process.

"Now it is time to fight for Lilly Ledbetter and the 150 million women in her position," she argued.

And Mikulski championed Rosa's Law, a citizen advocacy measure that banned the use of the term "mentally retarded."

"On behalf of all the children of the United States of America who are labeled, stigmatized and bear a burden the rest of their lives because of the language we use in the law books, my law simply today changes the phrase 'mentally retarded' to 'intellectually disabled' and we do it in health, education and labor policy without in any way negatively impinging on either the educational or other benefits that these children are entitled to," she said in a floor speech in the fall of 2009.

Becoming the longest-serving female senator won't be the last of Mikulski's firsts, either. Come March 17, 2012, she will become the longest-serving woman in the history of Congress.