* Kaczynski's conservatives tipped to win Sunday's election
* Family values guide Kaczynski's political decisions
* Bachelor Kaczynski was very close to late brother, mother
By Pawel Sobczak and Justyna Pawlak
WARSAW, Oct 23 (Reuters) - Arguably Poland's most polarising politician since the fall of communism, Jaroslaw Kaczynski is better known for wielding power behind the scenes than holding top jobs in government.
That won't change after Sunday's parliamentary election. With the party he founded, the conservative, eurosceptical Law and Justice (PiS) tipped to win, Kaczynski has fielded party loyalist Beata Szydlo, 52, as his candidate for prime minister.
But for Kaczynski, 66, twin brother of Poland's late president Lech who died in a government plane crash in 2010, an election triumph for PiS will be a deeply personal vindication.
A childless bachelor, Kaczynski's life has long been defined by politics. And though PiS commands a steadfast electorate of about 30 percent of voters, it has been in government for only two, tumultuous years since the twins established it in 2001.
There will be an element of revenge in any PiS victory, as well. Regaining power, he has long argued, would give him a chance to investigate more thoroughly the death of his brother and the nearly 100 others who perished in the plane crash in Russia on April 10, 2010.
PiS believes Poland's long-ruling, centrist Civic Platform (PO) party has obstructed the probe and blames it, at least indirectly, for the president's death.
"It is my obligation to my mother and my brother to seek to change Poland with all my strength, to fix what is wrong here. It is also my duty towards Poland," Kaczynski, a devout Catholic and Polish nationalist, told the conservative weekly wSieci.
"We will continue all of our efforts, from trying to uncover the truth about the Smolensk tragedy to defending democracy which is threatened by the current rule and to combating the de-christianisation (of Poland)," he said in the interview.
Kaczynski's supporters, many of them elderly, poorer and from small towns, believe he provides Poland's only chance to protect its traditional Catholic identity and its national sovereignty in the face of pressures from Europe.
"He has succeeded at forming a stable and lasting grouping that commands the conservative electorate," said Rafal Chwedoruk, a political scientist at the Warsaw University. "And he is unsinkable. He is a politician who has survived 20 years."
For Kaczynski's critics he is a xenophobic autocrat who demands absolute loyalty from his supporters and threatens to limit personal freedoms in Poland in the name of preserving national unity and conservative values.
"BRUTAL AND VENGEFUL"
Prime Minister Ewa Kopacz, whose PO has governed Poland since 2007, does not mince her words: "The Civic Platform is here so that we build a dam to stop those who want to turn Poland into a European museum of fanaticism."
PiS wants to enshrine more Catholic values in Polish law and more state control of the economy. Its lawmakers mostly oppose gay marriage and any access to abortion.
Kaczynski, mindful of his polarising image, has nominated the more restrained Szydlo for prime minister. Earlier this year he similarly stayed out of Poland's presidential election, instead fielding a young, relatively low-profile politician, Andrzej Duda, who then ousted the veteran PO-backed incumbent.
Kaczynski says his political priorities are clear: family first, then the nation and only then any other considerations.
Such priorities, he said this month, should guide Poland's approach towards Europe's migrant crisis. The arrival of Muslim refugees would, he said, threaten Poland's Catholic values and therefore they should not be admitted.
"We should help (the refugees) but in a safe way, financially," he said.
Kaczynski still lives in the same house, in a posh Warsaw suburb, where he lived with their mother after Lech moved out. She died in 2013.
Within the party, he was always seen as the strategist, while his brother took on more public roles, first as Warsaw's mayor and then as Polish president from 2005 until 2010.
"In the eyes of the voters, Jaroslaw will always be the inferior brother - cynical, brutal, domineering," Michal Krzymowski, a journalist with the Polish edition of Newsweek, wrote in a book about Kaczynski, published this year.
"As a politician, Jaroslaw is brutal and vengeful, but as a brother he is loving and ready for sacrifices."
The extent of Kaczynski's ties to his family became apparent to his close associates when Lech died.
Their mother was in hospital at the time, with a lung problem. Fearing the news might kill her, Kaczynski refused to inform her about the crash until she was well enough.
Every day, when he visited her in hospital, Krzymowski wrote, Kaczynski would change from his mourning clothes into a regular suit in a room next to hers. He has continued to wear black every day since his brother's death.
To circumvent her questions about Lech's absence from her bedside, he had fake copies made of Polish daily Rzeczpospolita. The paper described Lech travelling to Poland from a trip to Latin America by boat because of an Icelandic volcano eruption that had grounded flights in Europe at the time.
"The articles were crafted perfectly," Krzymowski writes. "They may not have been up to journalistic standards ... They were meant to soothe the mother." (Writing by Justyna Pawlak; Editing by Gareth Jones)
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