When representatives from some of the most powerful unions in the country arrived to march alongside the protesters on Wall Street last week, the “Occupy” movement was glad for the swell in numbers and the boost to their credibility.

But that didn’t mean they wanted leaders.

Protesters hold signs and march near Zuccotti Park as part of Occupy Wall Street. They have a loud voice but no leader. (T.J. Ortenzi/The Washington Post )

Since the movement began Sept. 17 as an encampment of dozens on Wall Street to protest corporate greed and unemployment, among other issues, “Occupy Wall Street” has prided itself on not having a leader. The movement calls itself a “people-powered movement” that uses “open, participatory and horizontal organizing.” But how long can it continue to be leaderless?

Some voices have already emerged to fill the leadership vacuum, including Slovenian philosopher Slavoj Žižek, who turned up at Zuccotti Park on Sunday to address the crowd.

Demonstrators listened to the former dissident for almost an hour as he lauded them for pointing out the “lies” that hold up American capitalist society, but warned them not to “fall in love” with themselves:

Žižek also told protesters they should embrace the tea party — another leaderless movement — instead of being their enemies. It was a sentiment similar to the one voiced by former White House green jobs adviser Van Jones last week, who told liberals that they ought to imitate the tea party, and that Occupy Wall Street was a good start.

Žižek’s voice was well received by protesters, but other leaders have gotten a different reaction.

When civil rights era icon Rep. John Lewis stopped by the Occupy Atlanta protests over the weekend, the human microphone used by protesters — a practice of repeating every phrase said so those in the back of the crowd can hear — couldn’t decide whether to let Lewis interrupt the scheduled talks and speak.

In footage that has emerged from Atlanta, it’s clear Lewis left the protests without being heard:

Conservative.com trumpeted the response to Lewis at Occupy Atlanta as proof the protesters were Marxists, writing that it was “reminiscent” of previous Marxist revolutions in history because it “purged and rejected [people] for the ‘good of the collective’ when their usefulness has expired.”

But even without leaders, the demonstrations have gotten some support in unexpected quarters. One unexpected supporter is Federal Reserve Chairman Ben Bernanke, who told the Joint Economic Committee last Tuesday that he understands the protesters’ frustrations

Alan Grayson, former U.S. representative for Florida’s 8th Congressional District,  has been another. In a recent TV interview, Grayson responded to a commentator who joked that a spokesman for the Occupy movement would need a bongo drum by saying, quite seriously: “If I am a spokesman for all the people in this country that we should not have 24 million in this country who cannot have a full-time job ... okay, I’ll be that spokesperson.”

Protesters, however, insist the movement does not need a leader or spokesman. They point to the leadership of the “general assemblies” held at the end of each day, a committee called the “Facilitation Committee” that runs each assembly, and the decisions that are made not by majority vote but by consensus.

Protester Matthew Swaye explained in a recent interview with MoxNews.com that it is “wonderful to have a leaderless movement,” because it helped disenfranchised groups be better heard.

“We’re not looking to put someone in office. ... This is the government!” Swaye said, gesturing behind him at the crowd of people. “It’s chaotic, but not random.”

But political organizers and leaders outside of the movement don’t think it can remain leaderless for long.

Jimmy Zuma, a disability rights advocate who started the online political journal Smart v. Stupid, wrote in Salon on Friday: “Right now you’re striving to be leaderless, but even without intending it, leaders will still emerge. Let it happen. Leaders are mostly a good thing. Never underestimate the power of a single person’s vision.”

Dr. Martin Luther King Jr. speaks to an audience with Rev. Andrew Young at his left on Feb. 7, 1968. (AP)

“There’s a difference between an emotional outcry and a movement,” Young said. “This is an emotional outcry. The difference is organization and articulation.”

Read more on the history of leadeless movements here.