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Former Colorado governor John Hickenlooper has announced his 2020 presidential bid.
The Democrat made the statement in a tweet, saying the country was "in crisis" and needed someone to "bring people together".
The post was accompanied by a video in which Mr Hickenlooper relates how he has stood up to his "fair share of bullies" during his career.
Mr Hickenlooper joins 14 other Democrats running for the top job.
He is the second governor to enter the field, following Washington's Jay Inslee who announced his bid last week.
US political analysts say he is sorely lacking in name recognition among voters in an already crowded Democratic field.
Mr Hickenlooper, 67, worked as a geologist before he was laid off and founded a brewpub chain in Denver. He then served as the city's mayor from 2003-2011 and went on to twice be elected governor.
His video, titled "Stand Tall", features the Rocky Mountain and touts his record in office and in the private sector.
"We beat the NRA," he says, describing gun control legislation that requires universal background checks on gun purchases, and bans on high ammunition-capacity magazines in Colorado.
The legislation came after a mass shooting at a movie theatre in the state "that once again tore the heart of our community," he says in his video, adding that "just offering thoughts and prayers would never again be sufficient".
Describing himself as a "doer", he says he brought together the oil and gas industry and environmentalists to create new methane emissions in the swing state.
He also says he convinced Democrats and Republicans to work together to expand the state's Medicaid health care programme that has achieved coverage for nearly 95% of all residents.
Speaking on ABC News on Monday, he said America is in "the worst period of division we've had in this country since the Civil War".
Asked how he plans to stand out in a growing field of Democratic challengers, he said: "I think I'm really the one candidate out there that has a very strong record of bringing people together and getting things done."
"One thing I've shown I can do again and again is create teams of amazingly talented people and really address these critical issues that are facing the country."
He plans to hold his first rally on Thursday in Denver.
Also on Monday, former attorney general Eric Holder announced that he would not seek the presidency, but would support the Democratic field.
Mr Holder, who was attorney general under ex-president Barack Obama, said that after travelling to 25 states in the past year he "found that the people of this country are better, and more caring, than these small-minded leaders would have us believe".