(CNN) -- Andrew Breitbart, the conservative blogger whose posting of a sexually explicit photo of former U.S. Rep. Anthony Weiner led to the congressman's downfall, has died, his attorney confirmed Thursday.
He was 43.
Joel Pollak, editor-in-chief and in-house counsel for Breitbart's website, Breitbart.com, posted a statement confirming his death.
"Andrew passed away unexpectedly from natural causes shortly after midnight this morning in Los Angeles," the statement read. "We have lost a husband, a father, a son, a brother, a dear friend, a patriot and a happy warrior."
Ed Winter, a spokesman for the Los Angeles County Coroner, said Breitbart was pronounced dead 19 minutes after midnight at UCLA Medical Center.
An autopsy is planned for Friday, Winter said, but the Los Angeles Police Department said it is not investigating the circumstances of his death.
Breitbart was the first to post Weiner's infamous Twitter photos last year, in which the married congressman appeared barechested and in his underpants in pictures sent to a woman online. Weiner eventually stepped down amid the scandal.
Breitbart's regular appearances on FOX News, his websites and his speeches to conservative groups made him a star on the right and a villain to the left.
Republican presidential candidates quickly responded to news of Breitbart's death. Former Sen. Rick Santorum called him a "powerful force" who was "constantly out there driving and pushing."
"What a huge loss, in my opinion, to our country and certainly to the conservative movement," Santorum said.
Former House Speaker Newt Gingrich tweeted: "Andrew Breitbart was the most innovative pioneer in conservative activist social media in America. He had great courage and creativity."
And former Massachusetts Gov. Mitt Romney called Breitbart a "brilliant entrepreneur, fearless conservative, loving husband and father."
Breitbart was a driving force in the conservative tea party movement. In a posting on the Tea Party Nation website, blogger Judson Phillips wrote that Breitbart was an "amazing patriot" who "relished fighting those who would destroy this great country."
Texas Gov. Rick Perry, a former GOP presidential contender, said Breitbart "fought for what he believed in, exposing government corruption and media bias. His spirited voice will be missed, but not forgotten."
Breitbart came under heavy criticism in 2010 for posting an edited and incomplete video of a speech by Agriculture Department employee Shirley Sherrod, who is black, appearing to say she discriminated against a white farmer looking for assistance.
Sherrod was forced to resign over the video, which appeared on another of Breitbart's websites, BigJournalism.com.
A full version of the speech showed that Sherrod had assisted the farmer. The department later offered her job back when it was clear she had been misrepresented.
Sherrod issued a brief statement Thursday saying only she was surprised by the news and that her prayers go out to Breitbart's family.
"The news of Mr. Breitbart's death came as a surprise to me when I was informed of it this morning. My prayers go out to Mr. Breitbart's family as they cope during this very difficult time."
Breitbart also posted video of a sting operation against the Association of Community Organizations for Reform Now, or ACORN, which showed conservative activists posing as a pimp and a prostitute seeking advice on how to set up a brothel.
The video prompted a groundswell of action against the organization, including a limited investigation by the U.S. Department of Justice and a slashing of funds from the federal government and several states. ACORN went bankrupt and closed its doors.
Breitbart got his start helping to run the original right-wing online media behemoth the Drudge Report and helped launch The Huffington Post before founding his own websites.
Drudge Report founder Matt Drudge on Thursday said Breitbart was a "constant source of energy, passion and commitment" in the site's early days and that the two "shared a love of headlines, a love of the news, an excitement about what's happening."
The statement on Breitbart.com Thursday included a portion of the new conclusion he wrote to his book, "Righteous Indignation":
"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.
"Three years ago, I was mostly a behind-the-scenes guy who linked to stuff on a very popular website. I always wondered what it would be like to enter the public realm to fight for what I believe in. I've lost friends, perhaps dozens. But I've gained hundreds, thousands -- who knows? -- of allies. At the end of the day, I can look at myself in the mirror, and I sleep very well at night."
CNN's Stan Wilson, Mark Preston, Richard Allen Greene, and Rachel Clarke contributed to this report.