Andrew Breitbart, a conservative U.S. blogger and activist who built a national media personality by putting undercover video on the Internet to bring discredit and disgrace to his liberal targets, died on Thursday in Los Angeles. He was 43.

The cause was apparently a heart attack, said his father-in-law, the actor Orson Bean. Someone saw Mr. Breitbart collapse on the sidewalk, Mr. Bean added, and when paramedics arrived they were unable to revive him. Mr. Bean said he believed Mr. Breitbart had a history of heart problems.

Mr. Breitbart was as polarising as he was popular. On the political Right he was hailed in the same breath with Rush Limbaugh and Matt Drudge as a truth-teller who exposed bias and corruption. On the Left, he was derided by many as a provocateur who played fast and loose with the facts to further his agenda.

Among his biggest coups was forcing the resignation of a New York Congressman, Anthony D. Weiner. Someone in Mr. Breitbart's network of tipsters and fans had emailed him sexually explicit photos that Mr. Weiner had taken of himself and sent to women online. Mr. Breitbart published some of the photos on his website, BigGovernment.com, igniting a firestorm that reached to the highest levels of Congress.

The move displayed two of Mr. Breitbart's defining features as a media personality: an eagerness to flout authority, and an innate sense for the viral news story. With the Weiner scandal, Mr. Breitbart, already a cult figure in the conservative media, only solidified his status as a force in his own right.

On Thursday, many of the luminaries he looked up to as a young man paid homage to him. Mr. Limbaugh called him “an indefatigable bulldog for the conservative cause”.

Mr. Breitbart was one of the most aggressive and most controversial users of blogs to disseminate political information and rumours, and his video methods were something new in conservative media. What Mr. Limbaugh was to the radio and what Mr. Drudge was to the Internet, Mr. Breitbart was to online video and images.

Andrew James Breitbart was born on February 1, 1969, in Los Angeles, a month before Gerry and Arlene Breitbart adopted him. He grew up in the exclusive Brentwood section of Los Angeles, an experience he called disjointing.

“Even though it was very much a keep-up-with-the-Joneses enclave, my parents seemed oblivious to all that,” he wrote. “When the first sushi restaurant popped up in our neighbourhood in the early 1980s, we had meat loaf that night.”

He was a graduate of Tulane University, having majored in American studies.

Though he described his parents as Republican, he said they were not overtly political.

“They came from the Silent Generation,” he said.

Silent Mr. Breitbart was not. As a conservative commentator he was a frequent presence on cable television shoutfests. He seemed to thrive on conflict.

In 2009, Mr. Breitbart started the first in a series of “Big” blogs with names like “Big Journalism”, “Big Hollywood” and “Big Government”. The websites gave Mr. Breitbart a big online perch of his own from which to unleash his assaults on liberal causes and figures.

One target, in 2009, was the community organizing group Acorn. A young conservative activist named James O'Keefe had come to Mr. Breitbart with undercover video of Acorn workers apparently offering advice on how to evade taxes and conceal child prostitution. In videotaping the encounter, Mr. O'Keefe and a companion had posed as a pimp and a prostitute. Mr. Breitbart eagerly published the tapes, and they went viral. In response, Congress ended grants to Acorn, and federal agencies severed ties with the group.

Mr. Breitbart earned a reputation for being playful but also selective with the facts. In an infamous case in 2010, he helped instigate the firing of an Agriculture Department official, Shirley Sherrod, by publishing a heavily edited video clip of her speaking at an NAACP event. Her comments, as edited, suggested that she had discriminated against a white farmer more than two decades ago.

In the full video, however, she could be heard saying that she had eventually helped the farmer and that she had learned from the experience that all people must overcome their prejudices. At Mr. Breitbart's death, she was suing him for defamation.

Many on the Left, like the liberal activist website Media Matters, often portrayed Mr. Breitbart as a caricature. Indeed, there was an element of performance art to what Mr. Breitbart did that could make him seem coarse and crude. He was often profane, and it was not uncommon to find him in rumpled shirts and torn jeans.

But in reality he was a more complex figure. He supported gay rights and once served on the board of GOProud, an organisation for conservatives dedicated to gay and lesbian causes. His friends described him as a deeply committed father to his four children and a loyal husband to his wife, Susie. And while he often railed against what he called corrupt mainstream media, he also knew that he needed them to further his own legitimacy. When he released the Weiner photos, he partnered with ABC News because, he said, he knew it would lend an imprimatur of authority.

He is survived by his wife; a daughter, Mia; and three sons, Samson, Charlie and William Buckley.

He was true to his reputation right up until he died. At 11:25 p.m. on Wednesday he sent out a Twitter message to someone who had taken issue with one of his comments. Mr. Breitbart had referred to him using a vulgarity “cause I thought you were being intentionally disingenuous”, he wrote. “If not I apologize.” — New York Times News Service

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