South Korean presidential candidate Moon Jae-In (C) of the Democratic Party gestures during a rally in Seoul on May 8. (Jung Yeon-Je/AFP/Getty Images)

The man set to become South Korea’s next president has earned an unusual nickname on the campaign trail. One of his rivals was called “Sprite” because he was considered refreshing and a female candidate was dubbed “Lovely.” But Moon Jae-in has been called “sweet potato” — because he’s considered stodgy and dense.

But a sweet potato can be comfort food, and after the turmoil of the past six months — when a huge corruption scandal triggered the impeachment of President Park Geun-hye — South Koreans want a known quantity.

Moon, the candidate for the liberal Democratic Party, has been buoyed by concern about President Trump’s unpredictability and by calls to wipe out the endemic corruption that brought down Park. He is widely expected to win the snap election being held Tuesday to replace her, putting a progressive in the presidential Blue House for the first time in a decade and heralding a sharp shift for South Korea.

The winner will take office Tuesday, without the usual two-month waiting period.

“This is the last challenge of my life, and I’m confident. I will muster all my efforts to be the president of all South Koreans,” Moon told supporters as he crisscrossed the country Monday, the last day of campaigning.

Supporters of Moon Jae-in, presidential candidate of the Democratic Party of Korea, wait for a rally to start. (Kim Kyung-Hoon/Reuters)

Moon had a strong lead in opinion surveys going into the election, regularly scoring above 40 percent while his two closest rivals struggled to get half that. Turnout for early voting was high. More than a quarter of the electorate had cast their ballots before polling day, a phenomenon expected to help Moon.

“When I look at his path in life, I think he is the best to represent us,” said Kim Ji-hyun, 31, who attended a recent Moon rally with her dog. “He’s very clean and he operates according to his principles. I think he will help South Korea to have its own voice.”

He is expected to name a new prime minister immediately and start appointing a cabinet, but Moon’s party does not control the National Assembly, potentially complicating the confirmation process.

Supporters at his rallies have lauded his track record after the corruption scandal involving Park, who is now on trial for bribery and coercion. Moon, 64, a human rights lawyer who has been in politics for only five years, is not a natural politician but one who arrived in this position through fate. His memoir is called “Destiny.”

Moon was born on the island of Geoje, off the coast from Busan, in 1953 to parents who had escaped from the North to the South during the Korean War.

Like many of his generation, he grew up poor but was able to attend a university. He became a student leader protesting the dictatorial government led by former general Park Chung-hee, the father of the impeached president. He was expelled and imprisoned.

But after completing his military service, he returned to his studies and passed the bar exam in 1980.

It was at this time that he met the like-minded Roh Moo-hyun, and the two of them set up a law office handling labor disputes and human rights cases in Busan.

Song Byung-gon, who worked as a paralegal in Roh and Moon’s law office until 2002, described the candidate as “prudent and gentle.”

“He was calm and quiet and I don’t remember seeing him get angry at work,” Song recalled. “He didn’t make jokes in the office, either.”

When Roh became South Korea’s president in 2003, he took Moon with him to Seoul, putting him in senior positions, including chief of staff.

During that period, Roh pushed ahead with the inter-Korean engagement started by his liberal predecessor Kim Dae-jung, and known as the “sunshine policy” — the idea being that if they could shine a little light into North Korea, they could lessen the divisions between the two countries.

Roh committed suicide in 2009 after becoming involved in a bribery scandal, and Moon won a parliamentary seat in Busan three years later. Within nine months, he was on the presidential ticket challenging Park.

Although he lost, he remained on the political scene and won the Democratic nomination after Park’s ouster in March.

As a candidate, Moon has been espousing progressive policies on the economy, promising to put together a huge stimulus package and to lessen the disparity between rich and poor.

Recent polls have put economic revival and cleaning up corruption at the top of voters’ priority lists for this election. Every generation of voter — from young graduates struggling to find jobs to baby boomers wondering how to support their elderly parents — is unhappy.

Moon’s core policy proposals include job creation, with the specific pledge to create 810,000 public-sector positions; reducing long working hours; improving transparency in government appointments; and strengthening regulations on the huge conglomerates that dominate corporate South Korea and have been implicated in recent corruption scandals.

But on social issues, he embodies Korean conservatism. During a televised debate, the leading conservative candidate asked him if he opposed homosexuality and same-sex marriage, and Moon said he did. This pronouncement was sharply criticized by LGBT groups but did not cost Moon politically — in fact, to support gay rights in South Korea would be politically damaging, even in 2017.

Although domestic issues have dominated this campaign, foreign affairs is much higher up the agenda than usual, in large part because of Trump’s election in the United States and the stance he has taken on both North and South Korea.

In a surprisingly detailed foreign policy statement released at the end of last month, Moon stated: “Nothing is more dangerous than letting others decide our fate.”

He has vowed to review the Park government’s decision to host a controversial American missile defense system and to resume economic cooperation with North Korea at a time when sanctions are all the rage.

Moon has said he would seek to reopen the South Korean-run factory park at Kaesong, on the North Korean side of the border that Park closed last year, saying it was violating international sanctions and channeling money to the Kim regime.

The possibility of a return to the sunshine policy — formulated in an era when North Korea had not conducted a single nuclear test — has raised concerns in Washington.

But the differences between Trump and Moon could be helpful, said Ralph Cossa, president of the Center for Strategic and International Studies’ Pacific Forum.

“You couldn’t have asked for stranger bedfellows than Roh Moo-hyun and George W. Bush, but the alliance survived and things moved ahead,” Cossa said. “In fact, this could be good news because it will force both of them [Moon and Trump] toward a middle path.”

Yoonjung Seo contributed to this report.