The conservative media publisher and activist who died Thursday at 43 was embraced by anti-tax, conservative tea partiers and reviled by liberals for his Internet investigations that led to the resignations of former New York Rep. Anthony Weiner and former U.S. Agriculture Department official Shirley Sherrod.
His loudmouth style was lionized by his fans for exposing government corruption and media bias. He was a colorful and often abrasive user of Twitter, including a final message that called a follower a "putz."
Breitbart was skilled at finding issues that pushed conservative buttons while pulling Internet traffic to his websites anchored to news aggregator Brietbart.com.
"I'm committed to the destruction of the old media guard," he once said. "And it's a very good business model."
It also was a radical departure from conservative voices of the past such as William F. Buckley Jr.
"I do what I do because the mainstream media chooses not to do it," Breitbart said. "The game of the left controlling the narrative ... is ending."
Larry Dietz, watch commander at the Los Angeles County coroner's office, said a cause of death was unknown and an autopsy was likely. Breitbart had suffered heart problems previously.
Republican candidates for president were quick to offer praise.
Newt Gingrich tweeted: "Andrew Breitbart was the most innovative pioneer in conservative activist social media in America. He had great courage and creativity."
Condolences also came from his liberal critics.
"We've disagreed more than we've found common ground, but there was never any question of Andrew's passion for and commitment to what he believed," said Ari Rabin-Havt of Media Matters, a liberal watchdog group.
Breitbart's website, bigjournalism.com, said Thursday he died of natural causes. He was walking near his house in the Brentwood neighborhood shortly after midnight when he collapsed, said actor Orson Bean, his father-in-law.
He was rushed to the emergency room at Ronald Reagan UCLA Medical Center. Bean said he could not pinpoint what happened.
"It's devastating," Bean told The Associated Press.
Breitbart's online profile called him a "mild-mannered family guy," However, Rick Santorum said he was a "powerful force."
"He will be what a huge loss ... for our country and certainly for the conservative movement and my prayers go out to his family," Santorum said. "I'm really sorry to hear it."
Mitt Romney posted to Twitter: "Ann and I are deeply saddened by the passing of (at)AndrewBreitbart: brilliant entrepreneur, fearless conservative, loving husband and father."
Sherrod, who is black, was ousted from her job as the USDA's state rural development director for Georgia in July 2010 after an edited video surfaced of her making what appeared to be a racist remark. She is seen telling an NAACP group that she was initially reluctant to help a white farmer save his farm more than two decades ago, long before she worked for USDA.
Missing from the clip was the rest of the speech, which was meant as a lesson in racial healing. Sherrod told the crowd she eventually realized her mistake and helped the farmer save his farm.
Once the entire video surfaced, Sherrod received numerous apologies from the administration - including from President Barack Obama - and Agriculture Secretary Tom Vilsack asked her to return to the department to work on civil rights issues.
She declined Vilsack's offer but later sued Breitbart, his employee, Larry O'Connor, and an unnamed "John Doe" defendant for "defamation, false light and intentional infliction of emotional distress."
A lawyer for O'Connor said Thursday that it is unclear whether the case will proceed for the other two defendants, who were in the process of trying to get the case dismissed from federal court.
In a statement Thursday, Sherrod said she was surprised to hear of Breitbart's death. "My prayers go out to Mr. Breitbart's family as they cope during this very difficult time. I do not intend to make any further comments."
Breitbart's websites also featured a 2009 hidden-camera video that brought embarrassment to the community group Association of Community Organizations for Reform Now. The videos show ACORN staffers offering advice on taxes and other issues to actors posing as a prostitute and pimp.
Those videos triggered a firestorm of criticism, with some ACORN employees appearing willing to support illegal schemes involving tax advice, misuse of public funds and illegal trafficking in children.
A Government Accountability Office report cleared ACORN of criminal activities.
Even so, public pressure led Congress to block previously approved funds from going to ACORN and to stop future payments. Roughly 10 percent of ACORN's funds came from federal grants and the group eventually disbanded.
Breitbart also sparked a controversy that ultimately led to the resignation of Weiner, whose problems began on May 28 when Bretibart's website posted a lewd photograph of an underwear-clad crotch and said it had been sent from Weiner's Twitter account to a Seattle woman.
Initially, Weiner lied, saying his account had been hacked. But he pointedly did not report the incident to law enforcement - a step that could have led the way to charges of wrongdoing far more serious than mere sexting.
Additionally, his public denials were less than solid - particularly when he told an interviewer that he could not "say with certitude" that he wasn't the man in the underwear photo.
Weiner's spokesman said the photo was just a distraction and that the congressman doesn't know the person named by the hacker.
The congressman denied sending the photo and said he had retained an attorney and hired a private security company to figure out how someone could pull off such a prank.
But Weiner dropped that story line on June 6, offering a lengthy public confession at a Manhattan news conference, acknowledging to online activity involving at least six women.
Breitbart seldom showed restraint in his vitriol to his critics and seemed to relish in the negative attention his antics earned him.
After Sen. Edward M. Kennedy of Massachusetts died in 2009, Breitbart tweeted, "Rest in Chappaquiddick" and called him "a special pile of human excrement." When critics questioned his tone, he tweeted they "missed my best ones!"
Breitbart is survived by his wife, Susannah Bean Breitbart, and four children.