Beck has become a soundtrack for conservative activists and members of the tea party movement, angry and frustrated with Mr. Obama and other Democrats in a highly charged election year. Beck suggests Mr. Obama is a socialist moving the country away from its ideals of limited government. Beck's critics contend that he exploits fear with conspiracy theories and overheated rhetoric.
Organizers say the "Restoring Honor" rally isn't about politics. It's to pay tribute to America's military personnel and others "who embody our nation's founding principles of integrity, truth and honor." It also is to promote the Special Operations Warrior Foundation, which provides scholarships and services to family members of military members.
If the gathering isn't political, no one told the Tea Party, which has organized busloads of supporters bound for Washington, hoping for a show of strength, CBS News Correspondent Wyatt Andrews reports.
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The event at the Lincoln Memorial - where 47 years ago King delivered his speech - is expected to feature 2008 vice presidential nominee and potential 2012 White House candidate Sarah Palin. Organizers have a permit for up to 300,000 people at the rally, although Beck has said he expects 100,000. Counter-rallies with the Rev. Al Sharpton and others also are planned.
Beck, 46, is a former "morning zoo" radio DJ who cleaned up after years of drug abuse in the 1990s and switched to talk radio. CNN's then-named Headline News network gave Beck his first TV home, and he switched to Fox in January 2009, shortly after Mr. Obama was inaugurated.
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His Fox show created an immediate sensation, as Beck spun his theories with an emotional fervor that Comedy Central's Stephen Colbert quickly dubbed "crank up the crazy and rip off the knob." MSNBC rival Keith Olbermann likens him to Lonesome Rhodes, the rags-to-riches everyman who spoke to a nation before he was unmasked as a fraud in the 1957 film "A Face in the Crowd."
In interviews, Beck sees himself more as broadcaster Howard Beale, the "mad as hell, and I'm not going to take this anymore" character in the 1976 movie "Network."
He was the driving force in stories about former Mr. Obama adviser Van Jones, who resigned after Beck publicized some of his past statements. Jones was linked to efforts suggesting a government role in the 2001 terror attacks and to derogatory comments about Republicans.
Beck's own statement last year that Mr. Obama had "a deep-seated hatred for white people" led to an advertiser boycott and protests from civil rights groups.
His Washington rally has attracted attention and criticism because it is taking place on the anniversary of King's speech and in the same spot. Beck has said it will be the moment when "we reclaim the civil rights movement."
His own Fox News colleague, Greta Van Susteren, said he should move his event. She said he should do it for sensitivity reasons, much as both she and Beck argue that an Islamic Center should not be built near the site of the World Trade Center, where terrorists struck in 2001.
"It does not help the country on so many fronts if we poke a stick in eyes," Van Susteren wrote on her blog.
Beck has said he wouldn't have picked the date if he had known about the anniversary. But he rejected attempts to move it, arguing that what he will say is consistent with King's "message of focusing on the content of a person's character above all else." King's niece Alveda King is scheduled to speak.
The size of the crowd will be a visible manifestation, beyond radio and television ratings, of how Beck has connected with people.
He was already the fifth most-listened-to radio talk show host when he moved to Fox, and he's since vaulted to third "with a bullet" behind Rush Limbaugh and Sean Hannity, says Michael Harrison, publisher of the trade publication Talkers.
More than his rivals, Beck has led the way in turning himself into a multifaceted brand. Besides the radio and TV shows, he goes on concert tours, he write books, he sells fans access to an "Insider" account for $74.95 a year and he sells his own advertising on his website.
"He's a model for a 21st century talk show host and businessman," Harrison said.
On his website, Beck offers access to "Beck University," a series of lectures. He sells hoodies touting his "9.12 Project," an attempt to recreate the national unity of the day following the terrorist attacks. He sells copies of his own Fusion magazine, so named for the "fusion of entertainment and enlightenment" that he calls his shows.
Beck and Fox colleague Bill O'Reilly occasionally bring their talk to stages with their "Bold & Fresh" theater tour.
And recently, Beck has begun a "morning prayer" podcast of inspirational messages that fans can access at 7:05 a.m.
On Thursday, he brought Father Terrence Henry of the Franciscan University in Steubenville, Ohio, to deliver a prayer - and promote Beck's rally.
"Like Paul Revere, you are spreading the alarm," Henry said.