Breitbart was walking last night near his Los Angeles home when he collapsed, said his father-in-law, actor Orson Bean.

"He collapsed on the sidewalk and the paramedics were there very quickly and they couldn't revive him," Bean told Reuters in a phone interview.

A friend of Breitbart told Reuters he had a history of heart problems and is believed to have suffered a heart attack.

The brash and outspoken blogger and commentator, who published politically inspired photos and undercover videos, was the center of several major news websites, including www.Breitbart.tv, www.breitbart.com and www.biggovernment.com.

Breitbart was a lightning rod who relished a role he cast for himself as an embattled conservative on the margins of the mainstream media he called "the Complex." Even so, he gained fans as a frequent guest on television news shows.

His work helped spark a number of prominent news stories in recent years. Those included undercover videos posted on his website about ACORN, a grass-roots group that offered housing assistance and other aid to the poor, and his role in bringing to public attention a sexually suggestive photo that Democratic U.S. Representative Anthony Weiner of New York posted through his Twitter page. That scandal eventually led to Weiner's resignation last year.

BROUGHT DOWN ACORN

In targeting ACORN, or the Association of Community Organizations for Reform Now, Breitbart posted videos in 2009 by conservative activists who secretly taped employees of the group giving tax advice to a couple posing as a pimp and a prostitute. The controversy led Congress to deny federal housing funds to ACORN, which disbanded in 2010. The former head of ACORN did not respond to an email seeking comment on Breitbart's death.

Breitbart faced widespread criticism when in 2010 his website posted a heavily edited version of a speech by U.S. Department of Agriculture official Shirley Sherrod that led to her forced resignation.

Sherrod, who is black, said her bosses at USDA pushed her to resign after Breitbart posted portions of a video in which she seemed to say she had discriminated against a white farmer. But in the full video of the speech that Sherrod gave, she had in fact said race should not matter.

Breitbart mentioned the Sherrod controversy last night in one of his last Twitter messages, in response to a back-and-forth discussion with Web users in which one person suggested he should apologize to Sherrod. "Apologize for WHAT?" Breitbart wrote back.

Breitbart cut his teeth in the freewheeling world of online media as an editor of the Drudge Report, working in Los Angeles far from the Beltway of Washington, D.C. He also worked with blogger Arianna Huffington, playing an early role at the Huffington Post, which was founded in 2005.

Matt Drudge, founder of the Drudge Report, said in a message on his website on Thursday that he remembered Breitbart as "a constant source of energy, passion and commitment."

"I still see him in my mind's eye in Venice Beach (in Los Angeles), the sunny day I met him. He was in his mid 20s. It was all there. He had a wonderful, loving family and we all feel great sadness for them today," Drudge wrote.

MEDICAL ISSUES

Amid suggestions that Breitbart had suffered a heart attack, Bean said he did not know Breitbart had any cardiac problems and the editor-in-chief of Breitbart.com declined to discuss any details about his health.

Breitbart was transported to a hospital where he was pronounced dead at 12:19 a.m. on Thursday, said Ed Winter, a spokesman for the Los Angeles Department of Coroner. An autopsy is tentatively scheduled for Friday. Winter declined to discuss any possible heart problems Breitbart might have suffered. "He had some medical issues, hadn't seen a doctor in over a year and we don't have his medical history yet," Winter said.

"We have lost a husband, a father, a son, a brother, a dear friend, a patriot and a happy warrior. Andrew lived boldly, so that we more timid souls would dare to live freely and fully, and fight for the fragile liberty he showed us how to love," a memorial page on Breitbart's websites said. The message said Breitbart "passed away unexpectedly from natural causes."

The leading Republican presidential candidates, conservative commentators and some liberals quickly reacted with sadness to Breitbart's death.

"Ann and I are deeply saddened by the passing of @AndrewBreitbart: brilliant entrepreneur, fearless conservative, loving husband and father," Republican presidential contender Mitt Romney said on his Twitter page.

A message from former Republican vice presidential candidate Sarah Palin posted on her Facebook page also praised Breitbart. "We are all stunned and saddened by the news of Andrew Breitbart's passing," she wrote. "Andrew was a warrior who stood on the side of what was right."

Even ideological opponents praised Breitbart.

"Andrew Breitbart was a conservative political combatant who was unafraid of his critics," tweeted Donna Brazile, Democratic Party strategist and former presidential campaign manager for Al Gore. "We battled on and off air, but he was a genius."

In his book "Righteous Indignation," Breitbart wrote: "I love my job. I love fighting for what I believe in. I love having fun while doing it. I love reporting stories that the Complex refuses to report. I love fighting back, I love finding allies, and - famously - I enjoy making enemies."

"At the end of the day, I can look at myself in the mirror, and I sleep very well at night," Breitbart wrote in the book.

(Additional reporting by Susan Heavey, Tim Gaynor and Mark Hosenball; Editing by Anthony Boadle)

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