An unpopular incumbent president and a scandal-plagued opposition leader. Two former justice ministers, one a fallen star and the other a neophyte.

South Korean voters were voting Wednesday to pick 300 members of parliament and decide whether President Yoon Suk Yeol will be able to advance his socially conservative agenda.

AFP looks at the four politicians who are key figures -- even though not all of them are personally on the ballot:

President Yoon Suk Yeol

Having won the 2022 presidential election by the narrowest margin in South Korean history, Yoon's time in office has been stymied by low approval ratings and an opposition-controlled legislature.

A former prosecutor and political novice, he shot to public attention for his uncompromising investigations of high-profile corruption scandals.

He's charted new directions in foreign policy as president but his administration has failed to deliver at home, with public dissatisfaction over a lacklustre economy fueling high disapproval ratings of his performance.

Additionally, outside of the party base, Yoon's "foreign policies have been generally unpopular," said Byunghwan Son, a global affairs professor at George Mason University.

South Korean presidents are elected separately but experts say Yoon will struggle to implement his agenda for the rest of his term, which ends in 2027, if his People Power Party (PPP) fails to win back control of parliament.

Lee Jae-myung

Lee lost the 2022 presidential election to Yoon but is widely expected to run again in 2027, despite facing a slew of probes into alleged corruption, including over purported illicit fund transfers to North Korea. He denies all charges and trials are ongoing.

A rarity among politicians in status-obsessed South Korea, Lee is a former child factory worker who rose to become a presidential contender by telling voters his working-class roots equipped him to fight inequality.

He was stabbed in the neck in January by a man pretending to be a supporter and has denounced South Korea's "politics of hate" -- while continuing to attack Yoon and the PPP.

But as leader of the opposition, Lee "has been equally as uninspiring as the president," Andrew Yeo, a politics professor at the Catholic University of America, told AFP.

"His focus is often steered towards blocking policies advanced by the PPP or criticising President Yoon rather than leading and governing his party."

Still, Lee would be seen "as the most likely next president" if his party wins by a landslide on Wednesday, Vladimir Tikhonov, professor of Korean Studies at the University of Oslo, told AFP.

Lee is is running in the Gyeyang constituency in Incheon, west of Seoul.

Cho Kuk

Once a rising political star, former justice minister Cho Kuk was tipped to run for president before an academic admissions scandal in 2019 engulfed his family. Yoon led the investigation.

After falling from grace and being sentenced to jail -- an appeal is pending -- he has made a dramatic comeback this election season.

He launched the Rebuilding Korea Party last month and, with a fiercely anti-government platform, the party has been polling strongly.

Cho's "popularity is almost entirely driven by those in their 40s and 50s who identify as liberals," Claudia Junghyun Kim, an international affairs professor at City University of Hong Kong, told AFP.

"They seem to be at the forefront of the increasing 'fandomisation' of South Korean politics."

Cho's party is only competing for the 46 seats out of 300 which are allocated by proportional representation.

The party was polling at nearly 30 percent approval last week, meaning -- if the numbers hold -- he could end up with 15 lawmakers in the 300-seat parliament, and be an effective kingmaker.

The rise of a third party "sends a message that people think the two main parties don't really represent them", said Linda Hasunuma, a political scientist at Temple University.

"He is the protest vote."

Han Dong-hoon

PPP leader Han Dong-hoon, a former star prosecutor, worked alongside Yoon on high-profile financial crimes and corruption cases, including the sale of now-defunct Korea Exchange Bank to Texas-based US private equity firm Lone Star Funds that resulted in a decade-long dispute.

Known for his tenacious and uncompromising style, he has conducted investigations into cases involving leaders of chaebols -- the family-controlled conglomerates that are pivotal to South Korea's economy.

He became justice minister under Yoon but resigned to take up the leadership of the PPP, where he is widely popular with the party's conservative base. He is not running in the elections because the party leader does not have to be a sitting lawmaker.

Critics accuse him of political bias and employing aggressive prosecutorial tactics that may not be suitable for the political arena.

Han's "popularity among the conservative wing of society represents its understanding of Lee and Cho being 'corrupt, hypocritical'," Byunghwan Son, a global affairs professor at George Mason University, told AFP.

He is an "antithesis to the Democratic Party" but his lack of political experience means he has a lot to prove and "his political stature would be easily threatened if PPP loses the election by a large margin", Son said.