Sri Lanka's former strongman president, who was ousted in January and is seeking a return to power as prime minister, is a polarising figure.
He won huge popularity among the majority Sinhalese for crushing Tamil separatist rebels in a no-holds-barred offensive in 2009 that ended a 37-year-long ethnic war.
But he is deeply unpopular with the country's Tamil minority, who voted overwhelmingly for his successor in January.
He has also been criticised for filling positions of power with his own relatives, some of whom now face charges of large-scale corruption.
His success in overseeing an end to the war in 2009 propelled him to a huge election win and a second term in office.
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He used his mandate to give himself more powers and remove a two-term limit on the presidency, but his decision to call a snap election for a third term prompted a stunning revolt from within his own party.
Rajapakse publicly blamed his defeat on lack of support from Tamils and Muslims, who together account for about a quarter of Sri Lanka's 20 million people and can tip the scales when the majority Sinhalese are divided. His opponents blamed nepotism and huge corruption.
The new government launched several investigations into charges Rajapakse and his family siphoned off billions of dollars.
His second son has also been implicated in a murder, although Rajapakse has defended his family, claiming a political vendetta.
"What ever you may say, we are not thieves and I don't have blood on my hands," he told a press conference last week.
Some of the strongest criticism of Rajapakse has come from outside Sri Lanka.
World leaders boycotted a Commonwealth summit he hosted in November 2013 to protest his refusal to investigate alleged war crimes by his troops.
When the United States and the European Union cut off aid, Rajapakse leaned heavily on China, Iran and Libya as well as other Asian nations for cash and arms to fight the Tamil Tigers.
A lawyer by profession, Rajapakse is strong believer in astrology.
During the current campaign he was nicknamed "lord of the rings" because he wore rings as lucky charms -- adding to the number as the campaign got tougher.
President Sirisena was a relative unknown even in Sri Lanka until he became the opposition's surprise choice to challenge his former mentor Rajapakse for the top job.
The 63-year-old became an unlikely rallying point for disaffected Sri Lankans after walking out of Rajapakse's government a day after sharing dinner with the former strongman president.
He ran on a promise of radical reforms including abolishing the executive presidency within 100 days and returning the country to a Westminster-style parliamentary democracy.
But his legislative agenda was stalled by a parliament dominated by MPs loyal to Rajapakse, who ruled for over a decade.
Sirisena has succeeded in introducing some reforms, depoliticising the police, judiciary, and other public services and restoring a two-term limit on the presidency.
But he has struggled to impose his authority over his United People's Freedom Alliance (UPFA) and was powerless to prevent Rajapakse from standing as one of the party's candidates.
Despite his mild-mannered reputation, he has made no secret of his feelings about his predecessor, saying he will use his executive powers to ensure Rajapakse will not be the next prime minister.
"If I had not won the presidency, I would be six feet under by now," he told told a public rally after his win, accusing the former leader of plotting to assassinate him and his family if he had lost.
Usually dressed in the white sarong and tunic favoured by Sri Lankan politicians, Sirisena appeals to a rural electorate while his main backer, the centre-right United National Party, is more popular in urban areas.
Unlike previous Sri Lankan leaders, Sirisena addresses international and regional gatherings in his native Sinhalese, even though he is competent in English.
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The son of a World War II veteran, Sirisena entered parliament in 1989 after settling in the eastern district of Polonnaruwa.
He was jailed for nearly two years after being arrested on suspicion of leading a revolt against the government in 1971 when he was just 20.
His vision for the country ties in closely with the free-market, investor-friendly policies of the UNP, which provided him with the political base to challenge Rajapakse.
Sri Lanka's outgoing prime minister is a champion of free enterprise who has managed to win economic and political support from both the West and regional superpower India in his eight months in office.
The 66-year-old was handpicked by Sirisena to lead a minority government after the shock ousting of the country's longtime leader Rajapakse in January.
His United National Party is the favourite in Monday's polls, giving him a shot at a fourth stint as head of government.
Wickremesinghe, a nephew of Sri Lanka's first executive president, Junius Jayewardene, almost became a reporter.
But a government takeover of his family's newspaper in 1973 deprived him of a newspaper career and he went into politics instead.
He rose to be prime minister in May 1993, when a suicide bomber assassinated president Ranasinghe Premadasa.
A similar incident arguably cost him the presidency in December 1999 when Chandrika Kumaratunga, the daughter of the country's well-known Bandaranaike dynasty, was wounded in a suicide bomb attack.
The attackers struck just three days before the presidential election and Kumaratunga went on to win narrowly on a wave of sympathy.
Wickremesinghe got his second chance in 2002, when he was credited with pulling the country out of its first ever recession and boosting economic growth to 4.0 percent.
In his campaign for a fourth term in office, he has pledged to overhaul Sri Lanka's dismal human rights record and create a "brand new country in 60 months".
Sri Lanka came in for strong criticism over its rights record under Rajapakse, who resisted UN calls to investigate allegations that over 40,000 Tamil civilians were killed in a 2009 military crackdown on separatist guerrillas.
Wickremesinghe has taken a more accommodating stance, pledging at his final pre-election press conference to address the issue.
"What I promise is a new country in 60 months (the term of parliament)," he said.
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