LEE JAE-MYEONG, 51

Mayor of Seongnam

A rising star among progressives, Mr. Lee calls himself the Bernie Sanders of South Korea. But he is more like President-elect Donald J. Trump in one respect: He uses Twitter, too. He has a huge audience there and has used his pointed comments to attack Ms. Park and her policies. He was one of the first major politicians to address the crowds of antigovernment demonstrators who have filled central Seoul on recent weekends. He says that Ms. Park “should be handcuffed” on criminal charges the moment she leaves office. Like the other progressives listed here, his positions on the approach to North Korea and missile defense are similar to Mr. Moon’s. Mr. Lee worked in a factory as a teenager and did not attend high school, but he taught himself, winning admission to a college and later passing the bar exam. Before running for mayor, he worked as a lawyer defending labor activists and political dissidents.

Image Ahn Cheol-soo. Credit... Chung Sung-Jun/Getty Images

AHN CHEOL-SOO, 54

People’s Party leader

A millionaire software mogul who leads a small opposition party, Mr. Ahn became a political star for his plain talk about equality and justice and his searing criticism of the existing political parties and big business. “Bill Gates wouldn’t have become Bill Gates if he were born in South Korea,” Mr. Ahn once said, accusing Samsung, Hyundai and other major corporations of creating “zoos” where they have shackled small entrepreneurs with slavelike contracts. Once considered a top contender for the 2012 election, he withdrew his candidacy, throwing his support behind Mr. Moon, with whom he has since parted ways. A medical doctor by training, Mr. Ahn made a fortune developing antivirus computer software. He says he wants to heal a country disillusioned with what he calls a corrupt and out-of-touch political and corporate elite.

Image Park Won-soon. Credit... Ed Jones/Agence France-Presse — Getty Images

PARK WON-SOON, 60

Mayor of Seoul

As mayor of the capital, Mr. Park is considered the second most powerful elected official in South Korea after the president. A former human rights lawyer, he is seen as a leader of the civil society movement and founded the country’s most influential civil and political rights group. He has won many landmark legal cases, including South Korea’s first sexual harassment conviction. He also campaigned for the rights of so-called comfort women, Korean sex slaves who were lured or forced into working in brothels for the Japanese Army during World War II. A tireless critic of what he calls growing social and economic inequality, he has pulled no punches in attacking Ms. Park, supporting huge rallies against her. Last month, he showed up at a meeting of cabinet ministers and shouted at them to “choose between the people and the president.”