- See also: MediaMatters
David Brock (1962-) is now the chief executive officer of MediaMatters, a group that monitors what it considers American conservative distortion in the news. He underwent an ideological conversion since he first came to Washington, D.C. in 1986, as a "conservative rebel." He introduces his autobiography, Blinded by the Right: the Conscience of an Ex-Conservative, as
This is a terrible book. It is about lies told and reputations ruined. It is about what the conservative movement did, and what I did, as we plotted in the shadows, disregarded the law, and abused power to win even greater power. 
Before leaving the conservative movement, a gradual process signaled by his registering as an Independent in 2000, he also had come out as a gay man. He later said “Had I come out of college as an openly gay man ten years later, I doubt I would have fallen in with the by-then transparently antigay GOP.”
Conservative critics, such as Byron York, then of the National Review, say that Brock's autobiography, in explaining where he lied for the Right, impugn his credibility. York describes his operation as funded by the usual suspects of the Left, and seeming more like a political campaign than a think tank.  David Horowitz attacked him for launching smear campaigns against the right, saying "I thought it interesting when George Soros and co. gave $2 million to a self-confessed liar to be the "liberal'" media watchdog." 
The Providence Phoenix stated the challenge, "Given his own history, Brock knows plenty about conservative pressure. But he’s also aware that questions continue to dog him in his new incarnation. Who is the real David Brock, and why should we trust him?" This article raised some concerns from the relatively small number of non-ideological media monitoring groups, such as Bryan Keefer, of CJRDaily.org, an online media-monitoring site created by the Columbia Journalism Review: "In terms of accuracy, they’re generally pretty good as far as they go,...But they are "self-consciously lefty.... They’re really only looking for things where liberals have been treated unfairly or where conservatives have gotten away with things." Brock said that he is in a niche, and not trying to do extensive content analyses and monitor standards and practices. "We have a more narrow mission," he says. "To work against undue conservative influence in the media."
More vexing for Brock is the cloud of suspicion that continues to hang over his work, in light of his ideological journey and confessed unethical behavior. "Once somebody has demonstrated himself to be an utterly untrustworthy liar," asks Rosenstiel of the Washington, DC–based Project for Excellence in Journalism, "why in the world would anybody think he has credibility now that he has switched teams?" Brock responded, " "If people don’t know me it can be difficult and it’s a totally legitimate and understandable question. In the history of ideological conversions, I’m not really aware of any that have changed twice." 
In October 2009, he said, of Fox News,"Our analysis of their programming has led us to the unavoidable conclusion that Fox is no longer operating as a “conservative news organization,” but as an outright partisan political operation – and brazenly so." 
Before college, he was an intern at the Robert F. Kennedy Memorial Foundation, and went to the University of California at Berkeley because it was associated with liberal political activism. In his first year there, however, the "campus was — although the phrase hadn't yet been coined — politically correct, sometimes stiflingly so." Working for the student newspaper, he was offended by the campus leftists' preventing the speech of speakers with whom they disagreed. In his sophomore year, he became an anticommunist, declared a history major with an emphasis on deplomacy, and began reading the neoconservative magazine, Commentary. He became more and more of a conservative, and eventually lost an election for editor-in-chief.
- David Brock (2002), Blinded by the Right: the Conscience of an Ex-Conservative, Crown Books, ISBN 0812930991, p. xi
- "Alumnus David Brock, founder of Media Matters", CalAlumniPride: UC Berkeley’s LGBT Alumni Club, 2 November 2009
- Byron York (28 May 2004), "David Brock Is Buzzing Again: And the gadfly’s main target is Rush (and Bush, of course)", National Review
- David Horowitz (1 December 2004), "Franken-Style Smears From David Brock’s Noise Machine", Frontpage Magazine
- Mark Jurkowitz, "Redemption tale: Former conservative-media poster boy David Brock is trying to do the right thing with liberal media watchdog Media Matters. Should we trust him?", Providence Phoenix
- Media Matters: Fox Is a Lethal 24/7 Partisan Political Operation, 23 October 2009
- Blinded, pp. 2-8