On the eve of his campaign kickoff, former Maryland governor Martin O'Malley released a video encouraging supporters to sign up on a Web site and "be the first to know" that he is running for president. The 23-second clip showed him strumming a guitar to the tune of -- what else? -- "Hail to the Chief."

The day before he is expected to announce his candidacy for president, former Maryland governor Martin O'Malley posted a video of himself playing 'Hail To The Chief.' (Video: Martin O'Malley/YouTube)

O'Malley, 52, announced his longshot bid for the Democratic presidential nomination on May 30 in Baltimore, where he served as mayor for seven years. He joined a Democratic field that now includes a formidable frontrunner, Hillary Rodham Clinton; a self-described democratic socialist from Vermont, Sen. Bernie Sanders; and a former Republican, Lincoln Chafee, a former senator and governor from Rhode Island. Here are a few things to know about O'Malley.

1) O'Malley got his start in politics working for Gary Hart.

A 20-year-old O'Malley worked for the former Colorado senator in eastern Iowa before the 1984 presidential caucuses, then headed to New Hampshire and other states as the race unfolded.

That contest has provided inspiration for O’Malley’s bid. Hart started as a major underdog against former Vice President Walter Mondale, barely registering in the polls when he entered the race. After a respectable showing in Iowa, Hart went on to win New Hampshire and became Mondale’s chief rival for the nomination.

O'Malley said in a recent interview that watching Hart's emergence in the race "absolutely informs my thinking." He also worked for Hart in 1988, when the Coloradan started as the Democratic frontrunner. His candidacy was derailed by a sex scandal.

Hart, now 78, has said he would support O'Malley's presidential bid. “I’m obliged to, if nothing else, because he supported me,” Hart said in an interview, adding that “it would be helpful to have generational change.”

2) O'Malley endorsed Hillary Clinton in 2008.

Shortly after he was sworn into office in 2007, O’Malley became the country's second sitting governor to endorse Clinton over then-Sen. Barack Obama of Illinois. At an event in Annapolis, O’Malley and Clinton sang one another’s praises. “She is ready today,” O’Malley said. “She is ready to lead.”

Reminded of his endorsement during a late-March appearance on ABC News’s “This Week,” O’Malley said that Clinton was the best prepared candidate “for those times,” adding: “I think our country always benefits from new leadership and perspective.”

3) O'Malley has a rock band.

O’Malley is the front man for O’Malley’s March, a seven-piece Celtic rock band. He sings and plays acoustic guitar and sometimes six-string banjo. The band’s heyday was during O’Malley’s time as a Baltimore councilman and mayor, when it played regularly in the city’s bars and around Maryland.

In the run-up to O'Malley's first bid for governor, the band announced its retirement, as O’Malley heeded advisors who said the late-night gigs detracted from his gravitas. But it didn’t take long for Martin and the boys to resurface: They appeared at O’Malley’s inauguration and have been playing several times a year ever since, even appearing at a White House St. Patrick’s Day party in 2012.

O’Malley doesn’t write as much original music as he used to, and the band’s demographic has aged considerably, but he still finds music to be a creative outlet. O’Malley has picked up a borrowed guitar several times as he visits early states, offering Democratic crowds a song after he delivers remarks.

Though perhaps best known for the progressive causes he pushed while governor, O’Malley initially won plaudits in government circles for his use of data to drive policy decisions.

As mayor of Baltimore, O’Malley pioneered CitiStat, a program that uses statistics to measure things such as pothole filling and overtime pay for garbage workers. Visitors came from all over the world to Baltimore City Hall to see how the award-winning initiative worked.

When O’Malley became governor, he took the program statewide, expanding it to hone strategies to clean up the Chesapeake Bay, reduce recidivism in state prisons and lower infant mortality.

“There’s not a doubt in my mind that this is the new way of governing and getting things done,” he said during a presentation in March at the Brookings Institution, where O’Malley said he sees a role for a similar initiative on the federal level.

5) O'Malley's mom works for Sen. Barbara Mikulski (D-Md.).

At age 87, Barbara O’Malley continues to work as a receptionist on Capitol Hill, where she is known as Mrs. O. She went to work for Mikulski 27 years ago, after Martin O’Malley worked on the venerable Democrat’s 1986 Senate campaign.

Mrs. O’Malley was the subject of a February profile in the Wall Street Journal, which reported that she is known for her acerbic wit and Spritz cookies.

6) O'Malley is  a practicing Catholic.

O’Malley regularly attends Mass and says his faith informs his views on issues such as the death penalty, which Maryland abolished in 2013.

During a recent speech in New Hampshire, O’Malley joked about his upbringing in “a mid-size Irish Catholic family” of only six children, adding: “People at Our Lady of Lourdes thought we were Lutheran spies.”

On some issues -- most notably same-sex marriage -- O’Malley has crossed the Catholic hierarchy. In 2011, he said he had come to see gay nuptials as an issue of “equal protection under the law.”

Speaking of the church leadership, O’Malley said: “Their job is to guard the tenets of the faith, and, you know, it’s understandable that the church, for that reason, that they’re slow to change.”

7) O'Malley presided over the introduction of casinos in Maryland.

You won’t find it on any promotional literature about O’Malley, but there would not be casinos in Maryland without him.

That’s not to say O’Malley is a fan of gambling. In fact, he once called slot machines “a pretty morally bankrupt way” to fund education.

Debate over gambling had paralyzed Annapolis during the tenure of O’Malley’s Republican predecessor, poisoning relationships among legislative leaders. So O’Malley sought to put the issue behind him early in his first term by getting legislative leaders to agree to let voters decide.

Since then, five casinos have sprung up across the state. A sixth -- at National Harbor, just across the Potomac River from Washington -- is scheduled to open next year, right around the time of the presidential election.

The possible 2016er on gay marriage, income inequality and more. (Video: Julie Percha/The Washington Post)