Thai election: a quick guide to the parties and major candidates, from Paetongtarn Shinawatra to Pita Limjaroenrat

Thailand's election is poised to be the most unpredictable in two decades.

There are 400 constituency seats in play and another 100 on a proportional basis for the lower house.

But an appointed upper house, or senate, of 250 members may tip the balance depending on the maths and will be pivotal in the vote for a prime minister.

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The magic number for a simple majority across the two chambers is 376, but expect complicated, uncomfortable alliances if no clear winner emerges. Pro-democrats hope to oust the ruling coalition of former army types and conservatives.

But a duo of elderly generals, including the 69-year-old current leader Prayuth Chan-ocha, stalk the race. They need to secure a minimum of 25 seats to enter the post-poll bid for the premiership - and with friends in high places there is a strong chance they can find a back door to power.

But if they cannot, no one is ruling out a coup or a court judgment to tip the balance.

Here are snapshots of the key people who will define the next period of Thai history.

The elder of the two generals with a combined age of 146 who have hobbled Thailand's democracy over the last two decades, Prawit was deputy prime minister in Prayuth's government.

While he fails to electrify audiences with his oratory, Prawit extols his political nous as his strongest hand in the election game and now regularly posts on Facebook promoting himself as an avuncular, compromise candidate for premier in a divided country.

Unmarried and fond of luxury watches of contested origin, he has hit the campaign trail wearing bomber jackets and tracksuits with what approximates gusto for a 77-year-old who has trouble walking unaided.

He heads the Palang Pracharath Party, which has tanked in the polls after an unremarkable period in government.

Prawit says he will not countenance reform of the 'section 112' royal defamation law, but he has fielded questions from political activists charged under the law promising no more coups - if he heads the next government.

A sign of desperation that his time in power may be up, or canny moves by Thailand's main political conductor? Foolish to ever rule him out.

Best campaign quote: "Xi Jinping never has to prove his capabilities by debating."

Thailand's irascible prime minister and former army chief, Prayuth left Palang Pracharath after a fallout with advisers to Prawit, his longtime comrade-in-coups.

He is running under the newly established United Thai Nation and needs just 25 seats from his supporters to be in contention to lead a new government, assuming the senate backs his cause.

Prayuth has been a central figure in Thailand's chaotic recent history.

As army chief he presided over the crackdown on Thaksin Shinawatra-aligned 'red-shirt movement' protesters in 2010, which killed scores on Bangkok's streets, and then four years later booted Thaksin's sister Yingluck out from office with a coup he promised would not happen.

Nine years on, his throwaway manner riles many across the country, including those who tack towards his ultraroyalist, conservative values.

But he has been busy on the campaign trail, explaining why at 69 he is still the "continuity" candidate Thailand needs. He has given rare interviews to independent Thai media and allowed people to spray water pistols in his face during the Songkran water festival.

But do not be confused. "Uncle Tu", as he is known, is not all cuddles - under his government pro-democracy activists have been hit with rubber bullets and pursued through the courts.

Best campaign quote: "Thailand is like an aeroplane - it needs an experienced pilot."

Aged 36, Paetongtarn carries the Shinawatra banner, a sign to her family's loyal farming base that she has the blessing of her father Thaksin and the Pheu Thai Party's social welfare policies will return if elected.

She is one of her party's three candidates for prime minister. If successful, she will be only the second Thai women leader as well as the youngest prime minister in the world.

An energetic campaigner despite being over eight months pregnant with her second child, Ung-Ing reaches the younger generations with her half-million followers on Instagram.

A political neophyte formerly fond of the Bangkok high life, she has surprised many pundits with her grounded approach on the campaign trail as well as her passionate stump speeches. But it remains unclear if she will try to be prime minister in the final shake-up.

Best campaign quote: "We are ready to rescue the country."

A rangy real estate mogul with a master's degree from the US and decades of experience in the property sector, the amiable Sreettha has emerged as a curveball PM candidate from the Shinawatra camp.

He has imposed himself on the campaign trail, seconding Ung-Ing through endless rallies, showing a common touch belying his wealth as the former CEO of Sansiri, Thailand's leading property developer.

Experts say he may be the real Pheu Thai candidate for prime minister - significantly, he does not carry the Shinawatra name that is a toxin to many in the conservative camp of Thai politics.

He has fronted Pheu Thai's ambitious - critics say uncosted and ruinous - promises to pour US$16 billion into the pockets of ordinary Thais. Those include a 10,000 baht (US$293) digital wallet handout to every Thai over age 16 to spend in their local area. He also pledges to slowly double the minimum wage to 600 baht a day and to offer university graduates a 25,000 baht starting salary.

Best campaign quote: "After every coup, the country's gone backwards."

Hero to Gen Z, Pita - or 'Tim' as he is nicknamed - heads Move Forward. Bold, articulate and with an easy confidence to match his Harvard education, some tout him as a possible foreign minister if they join a Pheu Thai coalition government.

But first Pita has a battle on to keep Move Forward's 6.3 million votes in 2019 under new election rules. The bete-noire of royalist conservatives, Pita and his party's shibboleth-smashing devotees are seen as the gravest threat to the establishment. His predecessor was banned from politics - do not rule out him (and/or his party) joining him. But with the older demographic narrowing, the long term looks in his favour.

Best campaign quote: "Where there's us, there are no uncles (Prayuth/Prawit) ... where there are uncles, there is no us!"

The personal poll ratings of Thailand's health minister are unimpressive, but he represents a bloc of wealth and political know-how from Buriram - home of his political mentor and one-time Thaksin ally Newin Chidchob.

Bhumjaithai Party is anticipated to emerge as a second or third party after the election, with kingmaking potential.

Anutin, 56, a construction tycoon and keen pilot, championed Thailand's recent decriminalisation of cannabis. While it is not uniformly popular, it has put Anutin on the front pages.

A royalist (he is also against amending the '112' law protecting the monarchy) but devoid of the hardline ideological baggage of the generals, analysts say his political shape-shifting gives him an edge over rivals of all political shades - depending what is promised to him.

Best campaign quote: "I am younger, more fresh and I understand politics in a democratic system."

This article originally appeared on the South China Morning Post (SCMP).

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