|Supporters of the yellow-shirted PAD urge people not to vote for any political parties in upcoming elections [Reuters]
The yellow-shirted People's Alliance for Democracy (PAD) emerged from a loose coalition of opponents to Thaksin Shinawatra, the ousted prime minister.
Founded in 2005 by Sondhi Limthongkul, a former media magnate, the PAD is a disparate collection of liberal democrats denouncing corruption and authoritarianism, and right-wing royalists who would welcome military rule with royal patronage.
The group adopted yellow as their trademark, a colour traditionally associated with the monarchy, in what they say is a show of allegiance to Thailand's king.
Its street protests in 2006 led ultimately to the military coup that toppled the then elected Thaksin, and it has led campaigns against subsequent governments it says are acting as Thaksin proxies.
The group largely disappeared from the scene during the subsequent period of military rule, but was re-formed when elections in late 2007 led to Thaksin's allies returning to power.
Its subsequent protests have culminated in court rulings that forced the resignations of successive prime ministers deemed to be Thaksin allies perpetuating his policies.
The PAD stood down after Thaksin's allies lost power in December 2008, and Abhisit Vejjajiva was appointed as Thailand's third prime minsiter in as many months.
But in 2010 the PAD's campaign of street protests escalated to a four-month siege of government offices and finally a blockade of Bangkok's two airports that lasted for more than a week, crippling the country's vital tourism industry.
The PAD's supporters are mainly urban, middle- to upper-class who are relatively rich compared to the majority of Thailand's rural population and are regarded as Thailand's traditional elite.
Thaksin's empowerment of the poor rural majority by implementing welfare programmes such as a universal healthcare scheme and cheap credit sparked fears in the country's elite that the wealth gap that gave them their lives of privilege could evaporate.
To counter, the PAD exploits Thaksin's weaknesses: corruption, heavy-handedness in dealing with alleged drug lords, accusations of manipulating the media and rumours of plans to turn Thailand into a republic.
Nobody knows who is really backing the PAD, but analysts suspect the group has deep pockets and is connected to some powerful business and political figures.
The group says it is funded by public donations, but there have been suggestions its main backers are anti-Thaksin business interests.
Some have also suggested it is supported by the monarchy, but the king has neither publicly backed nor condemned the group.
The PAD has a sophisticated media and public relations operation, owning a radio station, a satellite TV channel as well as running a slick and popular online operation.
Critics have said the group's name appears to be a misnomer as its opposition to the results of three elections show it is neither populist nor does it want representative democracy.
Instead, the PAD advocate scrapping the one-man-one-vote system in Thailand, and say only 30 per cent of parliament's members should be directly elected by the people. The remaining 70 per cent should be chosen from various occupations and professions and be appointed, they say. Similar ideas have been floated before, most notably in 1983.
Mass protests led by Yellow Shirts erupted in November 2013, calling on Prime Minister Yingluck Shinawatra - the sister of the ousted Thaksin Shinawatra - to resign. An amnesty bill backed by the government, which could have given Thaksin immunity from corruption charges he faces, outraged many - but the measure was rejected by Thailand's Senate.
Yingluck Shinawatra's survival of a no-confidence vote on November 28 did little to stem the demonstrations calling for her downfall, and protesters have occupied and besieged several government ministries in Bangkok.