Rampant is a 2018 South Korean period post-apocalyptic action horror film directed by Kim Sung-hoon. It was released on October 25, 2018.^[6][7] The film features a clash between exiled prince Lee Chung (Hyun Bin) and the Joseon minister of War Kim Ja-joon (Jang Dong-gun) with the backdrop of a spreading zombie plague. It received mixed reviews from critics and was a box office bomb, grossing $12.4 million worldwide against a production budget of $15 million.

In the Joseon dynasty, King Lee Jo is viewed as puppet to the nearby Qing dynasty of China by the Joseon nationalists. His son, Crown Prince Lee Young, plots to buy European arquebuses to drive away the Qing and at the same time removing his weak-willed father. The plot is exposed by War Minister Kim Ja-joon, who holds influence over the king and frames it as a rebellion. Kim meets the Europeans and learns that they have brought zombies (called "night demons"). The crown prince comes to his father and begs him to consider his proposal to oppose the Qing as they now have firearms but the impotent and stubborn King refuses to listen to his son. To save his men, the Prince commits suicide as penance so that his subordinates will be spared. Joseon forces destroy the European ship and retrieve the arquebuses, but a Joseon soldier is bitten by a zombie. He returns to his village, where he turns and spreads the infection. The zombies crave human meat and blood, are attracted by sounds, repelled by sunlight, and are stopped by decapitation or piercing of the heart, as well as separation of spinal vertebrae but methods of killing are inconsistent.

The crown prince left a request that his wife Gyeong-bin and unborn child be raised by his younger brother Lee Chung in China for their safety. Lee Chung had previously been left out of Joseon's order of succession as tribute to the Qing and grew up abroad in the prosperous Qing. Lee Chung returns with his companion Hak-Su, landing in Jemulpo, but is attacked by Joseon assassins sent by Minister Kim and other ministers, who are plotting a coup. The noise of the battle draws an attack by zombified villagers. Lee Chung and Hak-Su are assisted by local partisans, including Park Eul-ryoung, former lieutenant to the crown prince, and archer Deok-hee. The Jemulpo partisans ask Lee Chung to become crown prince, but he declines, wanting to return to China. Lee Chung awkwardly flirts with Deok-hee.

The only survivor of the would-be assassins is captured by Kim because he is infected. The ministers arrange for a concubine to be infected. She later turns and infects the king. Lee Chung arrives at the king's court, where he requests an army to crush the zombies. Paranoid, The king initially agrees as long Lee Chung does not want the throne but the ministers instigate him to rescind the order, claiming no zombie outbreak, only a civil rebellion. The Jemulpo partisans are arrested, while Lee Chung and Gyeong-bin are ordered to attend a banquet for a visiting Qing delegation.

At the banquet, the king fully turns into a zombie, and is slain by Kim, who unleashes zombies there in an attempt to kill members of the palace and the Qing delegation, then rule with all potential opposition gone. However, Kim is bitten by a zombie, leading to the ministers attempting to kill him. Kim slays them all, chops off his own hand to slow the infection, then madly declares himself king.

Gyeong-bin convinces Lee Chung not to flee but to protect the people, so Lee Chung, the royal guard and his Jemulpo allies freed from prison proceed to fight to prevent the zombies from escaping the palace and attacking the capital. Lee Chung and his allies plan to draw the zombies together into a gigantic fiery explosion at the palace. Kim kills Hak-Su and an infected Park, preventing the explosion. Lee Chung continues the same plan, battling a horde of zombies and the half-infected Kim. While doing so, he pours oil on the floor of the palace. Deok-hee fires a flaming arrow into the palace burning it down. Lee Chung retreats to the roof of the palace, only to find that Kim also climbed the palace.

Together, they duel with each other, Lee Chung being the victor. Reinforcements of soldiers and commoners later arrive to exterminate the rest of the zombies. Lee Chung recognizes that through the power of the people, the ruined Joseon still has hopes for existence, and elects to stay as the new King to lead his people rather than go back to Qing China. The movie ends with Lee Chung leads his troops to extinguish the remaining zombies at the port where the zombies first appeared.

Principal photography began on September 1, 2017^[14] and concluded on February 13, 2018.^[15]

The film is financed and distributed by Next Entertainment World, who was the primary backer of films such as Pandora and Train to Busan. It is directed by Kim Sung-hoon, who has worked with Hyun Bin in the hit film Confidential Assignment.^[16] On November 14, 2017, it was announced by distributor Next Entertainment World that actor Kim Tae-woo will fill the role of Crown Prince Lee Young, originally scheduled to be played by the late Kim Joo-hyuk.^[17][18]

The film was released domestically on October 25, 2018, alongside Grass and Hollywood film Crazy Rich Asians.^[6]

The film had already lined up theatrical releases in 19 countries. Release date for Philippines, Germany, UK, Vietnam, Myanmar, Singapore, Hong Kong, Macau, Thailand, Australia, New Zealand, US, Canada, Laos, Malaysia, Indonesia, and Cambodia is set within 2 weeks after domestic release date.^[19]