The BBC looks at key figures running in Thailand's first election since last year's military coup.
Mr Samak was a popular but controversial Bangkok governor
Samak Sundaravej leads the People Power Party (PPP), which was formed by lawmakers from ousted prime minister Thaksin Shinawatra's party, Thai Rak Thai.
Thai Rak Thai was dissolved by the Constitutional Court in May, for electoral violations, but Mr Thaksin's allies soon resurfaced under the PPP banner.
The 72-year-old Mr Samak, well-known for his fiery temper and abrasive manner, served as deputy prime minister alongside Mr Thaksin in 1995.
Elected Bangkok governor in 2000, he was then accused of corruption charges linked to two city contracts. He denies the charges but the case remains under investigation.
The veteran conservative has made no bones about the fact that he is running as Mr Thaksin's proxy and that he plans to bring him back.
"The military wanted to get rid of his party. They wanted not a single thing left over," he told the French news agency AFP. "I think that is unfair. So when he asked me (to run the party), I said 'OK'."
Mr Samak has adopted Mr Thaksin's populist platform and promised voters that he will work to improve the economy.
His political success comes despite long-standing allegations linking him to the suppression of a 1976 pro-democracy uprising, in which student demonstrators were killed. He denies these claims.
The Democrats, led by Abhisit Vejjajiva, are PPP's main rivals
Forty-three year-old Abhisit Vejjajiva, who leads the Democrat Party, has a rare reputation in Thailand for being a clean candidate.
Articulate and photogenic, the Oxford-educated former lecturer draws support from southern Thailand and from middle-class voters.
But he has struggled to reach the poor rural Thais that propelled Mr Thaksin to power.
The UK-born leader, who entered politics in 1992, is promoting a 99-day plan that includes many of Mr Thaksin's popular economic and social policies.
But he says that is not all his party has to offer.
"We would be a government that respects the law, that upholds the true principles of democracy, which allows the opposition to participate," he said.
Chart Thai leader Banharn could find himself in a strong position
Banharn Silpa-Archa heads Chart Thai, the third-ranked party, according to opinion polls.
Some analysts say Chart Thai could end up playing a key role in deciding the next government.
With both PPP and the Democrats unlikely to gain a majority, 75-year-old Mr Banharn could find himself in a position of considerable influence as the coalition partner of choice.
He has not publicly indicated which party he might back, describing Chart Thai as a "friend to all".
Mr Banharn commands considerable support in the central Suphanburi province, which he has represented since 1976.
He served as prime minister from mid-1995 until late 1996, and his government was widely seen as having paved the way for the economic crisis of 1997.
Critics accuse him of corruption, but he denies these claims.