Hillary Rodham Clinton officially launched her presidential campaign on Sunday. The announcement began with a video and a tweet. (Video: YouTube/Hillary Clinton)

This story has been updated.

Hillary Rodham Clinton entered the presidential race Sunday, saying she wants to fight for the economic futures of regular people and ending years of speculation about whether she would redeem the disappointment of her last, failed attempt to become the country’s first woman leader.

"Americans have fought their way back from tough economic times. But the deck is still stacked in favor of those at the top. Everyday Americans need a champion. And I want to be that champion," Clinton said in a video released Sunday. "...So I'm hitting the road to earn your vote. Because it's your time, and I hope that you'll join me on this journey."

The video served as Clinton's official announcement, though she only appears in it for less than half its roughly two-minute run time. Instead, viewers see a series of diverse and unidentified people. Women outnumber men, one man speaks Spanish and a gay couple is shown.

Clinton seems almost an afterthought, appearing at the end to tell viewers she is also ready to start "something new." A new Web site and accompanying Facebook page feature old photos and a link to donate to the campaign.

The announcement — designed to be as low-key as anything involving Clinton can be — contains no overarching campaign theme. Nowhere does Clinton succinctly say why she wants to be president, or why she would be good at the job.

Some of that detail will be filled in this week, as Clinton begins a series of small meetings with voters in Iowa. She will then travel to other early primary states for what advisers said will be mostly intimate sessions in restaurants and other modest venues.

Clinton's announcement sparked a number of nearly immediate attacks from her potential Republican rivals. In an email to donors, former Florida Gov. Jeb Bush wrote that, "Moments ago Hillary Clinton officially announced her White House bid — and it’s up to us to stop her." Texas Sen. Ted Cruz said that she "represents the failed policies of the past."

A former secretary of state, U.S. senator and first lady, Clinton enters as the prohibitive favorite among Democrats while also polling far ahead of any potential Republican rival now on the scene.

More celebrity than politician, Clinton is almost universally known. Nearly every American already has an opinion of her, whether good or bad.

Former U.S. senator and secretary of state Hillary Clinton announced that she’s running for president in 2016. Here's the Democrat’s take on women’s rights, Benghazi and more, in her own words. (Video: Julie Percha/The Washington Post)

Clinton summed her long and colorful biography in cheeky fashion when she joined Twitter in 2013: "Wife, mom, lawyer, women & kids advocate, FLOAR, FLOTUS, US Senator, SecState, author, dog owner, hair icon, pantsuit aficionado, glass ceiling cracker, TBD..."

The "to be determined" reference is now decided: a second attempt at the White House. Clinton has been running a shadow campaign for months, attacking Republicans and refining a Democratic base-friendly message heavy on themes of economic fairness and an equal shot at middle class success for all.

She has probably the best chance in history of becoming the first female U.S. president. That potential is woven throughout her emerging platform, with an emphasis on the advocacy for women and girls that has been the backbone of her professional life.

"Don't you someday want to see a woman president of the United States?" Clinton teasingly asked an audience of Democratic women last month.

A chief challenge of Clinton's early campaign will be to reintroduce or "re-brand" the candidate for a second presidential run. Advisers, including outside corporate ad-makers, have been at work on that project for months.

[The making of Hillary 5.0: Marketing wizards help re-imagine the Clinton brand]

The bar for success this time is high, set partly by the difficulties of one party holding the White House for three consecutive terms and partly by Clinton herself. Having fallen short last time, Clinton's second attempt was being measured against the first long before she made her 2016 bid official.

Many of the factors that contributed to her downfall in 2008 are still present, including Clinton's own limitations as a retail campaigner. Always more comfortable in the wonk trenches than on the campaign rope-line, Clinton is starting her 2016 campaign with smaller events intended to play to her strengths as an advocate. She had already been zinging congressional Republicans on Twitter while telling partisan audiences that she has experience working across party lines in Washington.

Noting the fifth anniversary of the Affordable Care Act last month, Clinton tweeted her support for the law along with a picture of her hugging Obama:

In her State Department memoir last year, Clinton credits her mother's perseverance in overcoming a hard-luck childhood with setting the comfortable middle-class course her own life would take.

Hillary Diane Rodham was born Oct. 26, 1947 in Chicago. She graduated from Wellesley College and Yale Law School, where she met Bill Clinton. After marrying in 1975, the Clintons lived in Arkansas where Hillary Rodham, as she was then known, practiced law and Bill Clinton eventually became governor.

When Bill Clinton was elected president in 1992, Hillary Clinton became the first American first lady to have had a fully independent career. Some of Hillary Clinton's oldest friends still rue that she gave up practicing law, and the maiden name she had always used, as Bill Clinton's national political career took flight.

[Read about Hillary Clinton's preparations for a White House bid.]

In the White House, Hillary Clinton's wide responsibilities for policy and secretive push for health care reform rubbed many people the wrong way. They also helped build the network of political loyalists who have sustained Clinton for more than two decades.

Bill Clinton's sexual relationship with intern Monica Lewinsky led to an impeachment effort, a family crisis and a national curiosity about the Clinton marriage that continues today.

Clinton was called a carpetbagger and a dilettante when she launched a campaign for an open Senate seat in New York in 2000, the final year of her husband's presidency. He campaigned for her enthusiastically and coached her early, halting efforts to connect with voters.

Hillary Clinton won largely on the strength of support from New York City Democrats, but once in office earned support in more Republican reaches of Upstate New York with dogged work on local issues.

Her ambitions reached beyond the Senate. In 2008, Clinton ran as the presumed favorite for the Democratic nod - but lost to the fresher face of Barack Obama and his more politically nimble campaign. Clinton has said the loss was one of the toughest times in her professional life.

As secretary of state during President Obama's first term, Clinton kept a punishing travel and work schedule that put her in the middle of national security decisions such as the killing of Osama bin Laden, the attempted policy "reset" with Russia and the U.S. stance amid the Arab Spring revolutions and their aftermath.

In her State Department memoir, "Hard Choices," Clinton noted that she was often the only woman at the table when she visited foreign leaders and diplomats.

[Earlier this year: Some Democrats worry that Hillary isn't ready.]

She was in Washington on Sept. 11, 2012, when militants overran the U.S. consulate in Benghazi, Libya, leading to the deaths of four Americans. The dead included Ambassador J. Christopher Stevens, whom Clinton had befriended and sworn in.

The event became a political debacle for the administration, with Republicans accusing the White House of trying to downplay the connections to terrorism in the weeks ahead of the 2012 presidential election. Multiple investigations have found no scandal, but plenty of bureaucratic bungling.

Her last weeks on the job in 2012 and 2013 were marked by a serious health setback, when she collapsed and hit her head. Clinton suffered a blood clot inside her head that required hospitalization.

One of her first public appearances after the accident was a Senate hearing in January 2013 that had been postponed because of her illness. Clinton wore special glasses to ease a temporary vision problem related to the injury. Under Republican questioning about the events in Benghazi, an angry Clinton said the focus on whether the attack was planned or spontaneous was irrelevant to the tragedy.

"At this point, what difference does it make?" she thundered. The line has haunted her since.

[Could Hillary's time at the State Department become a liability for her in 2016?]

Once out of the State Department, Clinton worked on her memoir, published last year, and gave speeches, both paid and unpaid.

In an interview to promote the book, Clinton talked about being "dead broke" when she and Bill Clinton left the White House. The remark was meant to show her empathy for people in financial straits but sounded tone-deaf for a woman who now has two mansions and commands up to $300,000 per speech. In another interview, Clinton sniped about Obama's cautious foreign policy approach.

"'Don't do stupid stuff' is not an organizing principle," Clinton told the Atlantic magazine. The criticism alarmed some Democrats, and Clinton quickly apologized to Obama.

She meets occasionally with her old rival and former boss, and is expected to tie herself to much of his agenda while distancing herself from some of the specifics.

Clinton's careful run-up to the campaign was thrown off course last month by revelations that she had used a private e-mail account and home-based server throughout her State Department tenure. The unorthodox arrangement meant that some of her communications were not preserved in real time, or at all.

She later said that she had handed over roughly 30,000 e-mails she deemed work-related, and had deleted about the same number she deemed personal. Congressional Republicans have cried foul, and a committee investigating Benghazi  is expected to call Clinton to testify about both the e-mail issue and the Libya deaths.