Five weeks from South Korea's election, it's down to a three-horse race.

Park Geun-hye's unprecedented ouster last month triggered a special election set for May 9. Late Monday, front-runner Moon Jae-in was confirmed as the candidate for the left-leaning Democratic Party of Korea, and Ahn Cheol-soo has all but sealed the nomination for his center-left People's Party. Hong Joon-pyo will represent Park's right-wing Liberty Korea Party.

Moon and Ahn will be trying to end nine years of conservative rule, while Hong will need to overcome the public anger that sent millions into the streets to protest against Park. Whoever wins faces a slew of challenges: Stagnating economic growth, North Korean nuclear threats, Chinese retaliation over the deployment of a U.S. missile-defense system, and reforming the family-run conglomerates, or "chaebol," that contributed to Park's downfall.