The founder of Thailand's yellow shirt political protest movement, which was behind the week-long occupation of Bangkok's main airports late last year, was shot and wounded early on Friday by unknown assailants.

Doctors at a Bangkok hospital were operating on Sondhi Limthongkul, 61, who founded the People's Alliance for Democracy (PAD)

Following are key facts about the PAD, a motley group of royalist businessmen, academics and a retired major-general that has been a main mover in Thailand's long-running political crisis, although it was not involved in the past week's violence:

* In Thailand each day is marked by a different color; yellow is the color for Monday, the day on which the King was born.

* Founded in September 2005 by media proprietor Sondhi Limthongkul, a disgruntled former business associate of the prime minister at the time, Thaskin Shinawatra.

* The PAD swelled into a major anti-Thaksin street movement, especially when it hooked up with Major-General Chamlong Srimuang, an ascetic Buddhist who led a successful people power uprising against military rule in 1992.

Its protests were key to the political turmoil that led ultimately to the 2006 coup against Thaksin.

* It restarted its street campaign in May 2008 and helped undermine two pro-Thaksin governments in power after elections held in December 2007.

The PAD's yellow-shirted activists occupied Government House from August to December 2008 and Bangkok's two main airports for about a week in November/December 2008, leaving hundreds of thousands of travelers stranded.

Current Prime Minister Abhisit Vejjajiva -- who was acceptable to the PAD -- was elected prime minister by parliament in December 2008 after defections by pro-Thaksin lawmakers.

* The PAD was not part of the political violence in Thailand over the past week, which involved Thaksin's red-shirted supporters.

PAD leaders said they decided to keep a low profile so as not to aggravate political tension, but they threatened to come onto the street if it looked as though government forces could not contain Thaksin's red shirts.

* The PAD's main draw card has been defense of the monarchy and 81-year-old King Bhumibol Adulyadej, regarded as semi-divine by many Thais, in the face of what they say is a bid by the Thaksin camp to turn Thailand into a republic. Thaksin and his supporters deny any challenge to the throne.

* There have been questions about the PAD's motives and backers. Its contempt for the results of general elections comfortably won by Thaksin or his allies has led to suggestions it represents neither the people nor democracy. PAD has said 70 percent of MPs should be appointed rather than elected.

The alliance says it is funded by public donations. Analysts suspect it is also bankrolled by anti-Thaksin business interests, parts of the army or even factions within the palace. * The PAD has a radio station, satellite TV channel, several sympathetic newspaper titles and a slick, popular website.

In the past it has shown an uncanny ability to keep itself in the public eye and drive the domestic political agenda, jumping on issues such as a dispute with Cambodia over a 900-year-old Hindu temple to whip up anger against a pro-Thaksin government last year.