(Reuters) - The elderly man dressed in homespun cotton looks like a kind-hearted grandfather from a rural Thai soap opera.
But it would be unwise to underestimate Chamlong Srimuang, a key figure in Thailand's turbulent recent history, or the "yellow shirt" army he commands.
"We have successfully overthrown three prime ministers, which proves our track record is excellent," says Chamlong, co-leader of the People's Alliance for Democracy (PAD), whose yellow-clad members shut down Bangkok's international airport in 2008.
"We have the ability to overthrow another government again if need be."
That last claim might have rung hollow before June 1, when thousands of protesters from the long-dormant PAD blockaded the Thai parliament.
That halted debate on a reconciliation bill which the yellow shirts believe will bring home their arch-enemy, former Prime Minister Thaksin Shinawatra. He was toppled in a 2006 military coup after months of PAD street protests and now lives in self-imposed exile.
The PAD's return brought back memories of a tumultuous 2008, when yellow shirts seized government offices, fought street battles with police, and occupied Bangkok's main airports for eight days. Amid that turbulence, two pro-Thaksin prime ministers were forced to resign by the courts.
The Asian Human Rights Commission accused the group in 2008 of "fascist qualities" and said it posed "grave dangers" to Thai democracy, but they kept a low profile after Thaksin's sister, Yingluck Shinawatra, became prime minister almost a year ago.
A political novice, Yingluck traded on the name and populism of her brother, loved by Thailand's rural and urban poor masses.
But the yellow shirts are seeking a comeback now that Thaksin's allies are gaining momentum for a national unity bill likely to clear his name, expunge his graft conviction and return $1.5 billion of his assets.
Opposition politicians and analysts warn of a "reconciliation war" if parliament passes two bills: one to grant an amnesty to political offenders, the other to amend a military-drafted constitution that Thaksin says is undemocratic.
"We will give Yingluck's government time," says Chamlong, a former general who in May 1992 led a popular uprising against military dictatorship that claimed dozens of lives. "But if she wants to go ahead with her reconciliation plans, then she has to take responsibility for the consequences of her decision."
Despite such fighting talk, blocking the bills would be a big undertaking for a PAD that seems fractured, less popular and struggling to remain relevant.
"It's too early to tell if the yellow shirts can attract the same support they did before, but right now, they are weak," said Kan Yuanyong, director of the Siam Intelligence Unit think tank.
Crowd-pulling yellow shirt leaders, such as media mogul Sondhi Limthongkul, retain an almost cult-like following. Sondhi survived an assassination attempt by mystery gunmen three years ago and his blood-splattered clothes are prominently displayed at the PAD's Bangkok headquarters in a gold frame.
But he has since been caught up in complex legal cases that include appeals against jail terms for multiple counts of securities fraud and defamation and charges of terrorism over the airport blockades.
PAD supporters say Sondhi's troubles have dented morale but not broken it.
"Sondhi is not critical to the survival of the PAD," says Saenkam Chonchadathan, a university student and member of the Young PAD group. "Without him, the movement would still exist."
Perhaps more essential to the yellow shirts are Thaksin's powerful enemies in the royalist establishment and military, which refused government orders to tackle the PAD in 2008, two years after it overthrew Thaksin in a coup.
It also needs the help of Bangkok residents, wearied by seven years of unrest that has hurt investor confidence and paralyzed parts of the capital's commercial and business districts.
Many groups have splintered off from the core PAD movement, disagreeing with its ultra-nationalist tones. But they still see eye-to-eye with the yellow shirts on many issues.
Other sub-groups say they do not necessarily share the PAD's anti-Thaksin sentiment but are ready to join forces if they feel their business interests or the country's political and economic stability are under threat.
The PAD has held rallies over a territorial dispute with Cambodia that fizzled out and its campaign call to back no one in the 2011 election backfired because the protest ballots were cast mostly by supporters of the then-ruling Democrat Party. This helped Yingluck's Puea Thai Party romp to victory.
It also soured the marriage of convenience between the PAD and the Democrats. Today, they share a disdain for Thaksin and a similar support base, but little else.
The two sides "have never been friends", says PAD co-leader Chamlong.
Even so, the yellow shirts may be forced to rekindle that relationship and get the Democrats' supporters and their friends in big business behind another street campaign.
"The yellow shirts need the Democrat party," said Kan of the Siam Intelligence Unit. "Otherwise they will not survive."
A yellow shirt revival also raises the potential of conflict with a red-shirted pro-Thaksin movement that helped propel Yingluck to power.
Formally known as the United Front for Democracy Against Dictatorship, its months-long anti-government protest in Bangkok in 2010 ended with a military crackdown in which 92 people died.
Parliament agreed this month to suspend debate on the reconciliation bill and a constitutional change bill until the new house session in August after the Democrats, Thailand's main opposition party, complained the changes could undermine Thailand's revered monarchy.
Tensions have temporarily eased, but the fate of the government's constitutional change bill will be decided by the court next month. If given the green light to go ahead, anti-government groups will be ready to step in.