Profile: Jaroslaw Kaczynski
Jaroslaw Kaczynski stood as a candidate in Poland's presidential elections following the death of his twin brother Lech, who was killed in a plane crash on 10 April.
He trailed centre-right opponent Bronislaw Komorowski in the first round, but gained enough votes to force a second-round run-off on 4 July.
Mr Kaczynski, 61, is a combative conservative former prime minister who was voted out of office three years ago.
But following the plane crash which killed President Lech Kaczynski, he has presented himself as a man of compromise.
The disaster, in which 96 people were killed, including many senior Polish figures, is thought to have boosted both Kaczynskis' popularity.
Jaroslaw Kaczynski was born in 1949, 45 minutes before his brother Lech.
The twins became child stars, acting in The Two Who Stole the Moon, a Polish film that was released in 1962.
Both took part in the Solidarity movement that opposed communism, though they fell out with Solidarity leader Lech Walesa after he became Polish president in 1990.
In 2001, they formed the Law and Justice Party to unite Poland's right wing.'Great responsibility'
The pair's staunch defence of Polish sovereignty and emphasis on traditional Catholic values won them support in rural Poland, but provoked stiff opposition from many younger and urban voters.
Lech Kaczynski was elected president in 2005, and the twins held the two top jobs in Polish politics after Jaroslaw became prime minister the following year.
The right-wing coalition, which collapsed in 2007, had difficult relations with the EU and Russia.
Lech Kaczynski had been expected to run for re-election in October against Mr Komorowski, though opinion polls at the time suggested he would lose.
In the weeks that followed the crash, Jaroslaw Kaczynski announced that he would stand in an earlier vote in order to continue his brother's mission.
"Poland is our common, great responsibility," he said.
"It demands that we overcome personal suffering to take action despite a personal tragedy."
On 18 June, when the twins would have celebrated their 61st birthday, Mr Kaczynski laid a wreath on his brother's tomb.
Mr Kaczynski had accused his centre-right Civic Platform opponents of selling out to foreign investors and neglecting poorer Poles.
Mr Komorowski and his patron, Prime Minister Donald Tusk, had portrayed Mr Kaczynski as a populist who would wield his presidential veto to block economic reforms.