A few years ago, Suthep Thaugsuban was a suit-and-tie wearing deputy prime minister of Thailand and a senior executive of the country's oldest political party.

Now, at 64, the career politician has ditched his office attire, distanced himself from the opposition Democrat Party and found a new calling as a street fighter.

Suthep is the mastermind of Thailand's latest round of street protests and has vowed to topple Prime Minister Yingluck Shinawatra by taking over every government ministry.

After storming the Finance Ministry earlier this week and camping there two nights, Suthep led protesters for a fourth day Wednesday in what he calls a people's power uprising.

Whistle-blowing throngs massed inside or around at least six of the government's 19 ministries, although they left half of them after a few hours. One large group led by Suthep entered a sprawling government office complex that houses the Department of Special Investigations, the country's equivalent of the FBI, and prepared to camp there overnight.

"We like peaceful methods," Suthep told reporters, his voice hoarse from speaking above the crowd's roar. But he added, "If we don't succeed, then I am prepared to die in the battlefield."

"The people will quit only when the state power is in their hands," he said. "There will be no negotiation."

The brash threat is the boldest challenge yet to Yingluck's embattled administration, and it has raised fears of fresh political violence in the divided Southeast Asian nation.

Yingluck has repeatedly said she wants to avert violence and offered to negotiate an end to the crisis. So far, security forces have not even fired tear gas to prevent protesters from forcing the closure of multiple government offices. A warrant was issued for Suthep's arrest, but he has ignored it.

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Anti-government protesters wave Thai national flags as they march toward the Labour Ministry in Bangkok on Wednesday. (Athit Perawongmetha/Reuters)

"We must not regard this as a win-or-lose situation," Yingluck told reporters at Parliament. "Today no one is winning or losing, only the country is hurting."

Protesters want Yingluck to step down amid claims she is a proxy for her brother, billionaire former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 military coup but remains central to Thailand's long-running political crisis. Thaksin lives overseas to avoid a corruption conviction that he says was politically motivated.

In broad terms, Thailand's political crisis pits Thailand's elite and the educated middle-class against Thaksin's power base in the countryside, which benefited from populist policies designed to win them over. Thaksin's party is the most successful in modern Thai political history. He became the only prime minister to serve out a full term, and Thaksin or his allies have won every election since 2001. The Democrats were crushed by Yingluck's ruling party during the election that brought her to power in 2011.

On Sunday, more than 100,000 demonstrators took to Bangkok's streets for the largest rally in years, uniting against what they call the "Thaksin regime." The crowds Wednesday were far lower — in the tens of thousands — indicating that Suthep is unlikely to meet his goal of bringing down the government this week without more popular support, or judicial or military intervention.

Dealt with protesters before

But Suthep has proven a few things during his time in the street. Notably that he is tenacious and unpredictable.

Before becoming a protest leader, Suthep was the man assigned to deal with unruly anti-government protesters when the Democrats were in power.

In 2010, when Suthep was deputy prime minister under a Democrat government, he signed an order that authorized the military to disperse Thaksin's "Red Shirt" protesters who had occupied a large section of downtown Bangkok. The eight-week protests and crackdown left more than 90 people dead and about 1,800 injured. It was Thailand's worst political violence in decades.

Now that the tables have turned, many fear that Suthep is leading Thailand back to volatility.

"Have we learned our lessons? Is history going to repeat itself?" Bangkok Post editorial page editor Sanitsuda Ekachai wrote in a column Wednesday. "On one side are the protest leaders looking for blood. On the other side is the government — unrepentant for its abuse of majority power — set to fight to the end. The scenario ahead looks gloomy indeed."

Did the dirty work

For years, Suthep was the behind-the-scenes dealmaker for the Democrat Party, whose public face was the clean-cut, Oxford-educated Abhisit Vejjajiva. Abhisit was prime minister during the 2010 crackdown.

The party often relied on Suthep to do its dirty work, according to a U.S. Embassy cable from 2008 leaked by Wikileaks.

"Several Democrats have privately complained to us that he engages in corrupt and unethical behavior," the cable said. "While Abhisit appears publicly as an ethical intellectual, Suthep serves as the party's backroom dealmaker."

The anti-government campaign started last month after Yingluck's ruling Pheu Thai party tried to pass an amnesty law that would have enabled Thaksin to return home as a free man. The Senate rejected the bill in a bid to end the protests, but the rallies gained momentum.

Suthep seized the opportunity to step into the spotlight. He resigned as an opposition lawmaker in mid-November to lead the demonstrations, which morphed into a wider anti-government campaign with ever-shifting strategies.

After initially pledging to lead a law-abiding show of "civil disobedience," Suthep switched to the tactic of occupying government offices.

Rejects new elections

At first, he called for Yingluck's resignation but now says he won't rest at that. He says his goal now is to replace the government with a non-elected council — an apparent call for less democracy, not more. He says the change is necessary to uproot the Shinawatra political machine from Thai politics.

Suthep has rejected new elections, which the opposition Democrats are certain to lose.

He insists that he has no ambition to be prime minister, and on Wednesday said he is settling into his new role.

"Being a member of Parliament, you wear a suit and tie, you act smart in an air-conditioned room. When you stand up and say something, people applaud," a tired and sweating Suthep told reporters, dressed in his now-regular outfit of all black.

"Here, you speak until you lose your voice," Suthep said. "But I've made up my mind that I'd rather work here for the people."