"It looks like a heart attack, but no one knows," Breitbart's father in law, Orson Bean, told the Los Angeles Times.

"He was walking near the house somewhere.... He was taken by paramedics to UCLA, and they couldn't revive him," Bean added.

A statement posted to Breitbart's website Thursday said that he died of natural causes, an assumption Los Angeles police have been working under.

Breitbart ran the news aggregation website, as well as a number of other conservative outlets, including Big Government and Big Journalism. He was also an influential part of the early days of both the Drudge Report and the Huffington Post, two of the web's most-visited news sites.

Breitbart is survived by his wife, Susie, and four children.

Breitbart’s brash conservatism and propensity to publicly tussle with his critics kept him close to controversy, but also contributed to framing some of his biggest accomplishments.
Perhaps his most notable achievement was in breaking the story that led to the resignation of former Rep. Anthony Weiner (D-N.Y.).

In June, Breitbart uncovered an X-rated photo of Wiener that the lawmaker had mistakenly made public over Twitter before quickly removing it.

Breitbart even crashed the press conference in which Weiner admitted the photo was his, taking the stage to claim responsibility for what was about to unfold ahead of the former congressman.

The conservative activist was also involved in promoting high-profile stories like conservative filmmaker James O'Keefe's investigations into ACORN and National Public Radio.