Andrew Breitbart died early this morning of natural causes, according to a report on his website. That initial report has been confirmed by the LA Coroner, according to ABC and The New York Times. Breitbart's father-in-law, Orson Bean, told the AP that Breitbart was out walking after midnight when someone saw him collapse and called for help. "Breitbart had suffered heart problems a year earlier, but Bean said he could not pinpoint what happened."

Breitbart was an editor for The Drudge Report then helped launch Huffington Post. He later created his own network of websites, including Big Journalism and Big Government. Breitbart, a father of four, turned 43 last month.

The New York Times' Jeremy Peters described the polarized views of Breitbart in a June 2011 profile:

The stories and videos Mr. Breitbart plays up on his Web sites — which include Big Government, Big Journalism and Big Hollywood — tend to act as political Rorschach tests. If you agree with him, you think what he does is citizen journalism. If you don’t, his work is little more than crowd-sourced political sabotage that freely distorts the facts.

Talking Points Memo is publishing condolences from Fox News' Sean Hannity, GOP presidential hopeful Rick Santorum and others, including liberal website Media Matters, which said:

Media Matters has a long history with Andrew Breitbart. 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.

Our thoughts and prayers are with his family today.

James O'Keefe tells me he's putting out a statement shortly. Breitbart described his first encounter with O'Keefe, saying he saw similarities between them:

What is immediately clear to me is that James is passionate and wants to expose corruption. As is his gutsy partner in exposing crimes, Hannah Giles. James is like me: he’s idealistic, right–leaning, and doesn’t pretend he’s a neutral and objective journalist. (No one’s “objective.”)

Reaction to Breitbart's death:

Highlights from recent coverage:

Huffington Post apologizes to Andrew Breitbart for video doctoring accusation (August 2011)

  • The Huffington Post has apologized to Andrew Breitbart for a story that accused him of doctoring a video to stir a “false controversy” over a CBS reporter’s question in a White House press briefing.

Conservatives tip off Breitbart because ‘I’m willing to march through the fire with them’ (June 2011)

  • "Andrew Breitbart got his vindication and an apology when U.S. Rep. Anthony Weiner admitted online dalliances with several women."

Shirley Sherrod Story Shows Waves and Undercurrents in a Media Tsunami (July 2010)

  • “We have come to the conclusion we were snookered by Fox News and Tea Party Activist Andrew Breitbart into believing she had harmed white farmers because of racial bias."

Breitbart, Carlson ‘a new breed of conservative pseudo-journalists’ (July 2010)

  • “If buzz is your measure, it’s been a great week for the conservative new media.”

Breitbart: “I’m sorry, mainstream media. It’s over.” (February 2010)

Huffington was, in some sense, a model for Breitbart (May 2010)

  • “I knew that I wanted to get into what I had helped create for Arianna, but I wanted to do it from a different perspective."

Steve Myers and Andrew Beaujon contributed to this post.