Set at the start of the 17th century, three years after the end of the Imjin War, Kingdom takes place in a fictional, medieval-inspired Joseon (modern-day Korea) and blends political thriller and elements from zombie horror.

The story follows Lee Chang, the Crown Prince of Joseon, who attempts to investigate the mysterious illness recently afflicting the King, only to find himself caught in the middle of a deadly epidemic ravaging the kingdom.

[11][12][13][14] A special feature-length episode of the series, titled "Ashin of the North", was released on July 23, 2021, presenting a focus on the supporting character played by Jun Ji-hyun.

The episode acts as a sidequel to the second season of Kingdom and explores the backstory of Ashin, the mysterious character Lee Chang's group encountered on their journey north to discover the origins of the infected.

[15][16] Set during the Joseon Dynasty, three years after the Japanese invasions, the story follows Crown Prince Lee Chang who, along with his subordinates, finds a zombie plague is ravaging the countryside amidst a brewing political conspiracy.

[34] On January 7, 2021, a castle on the filming set of Kingdom: Ashin of the North caught fire as a staff member attempted to melt the snow using a torch lamp.

[35] Screenwriter Kim Eun-hee began thinking about the story behind the series in 2011, wanting to reflect the fears and anxiety of modern times through the lens of the historical Joseon period.

[36][37] Originally, the creator thought it would be difficult to portray the story in a television series format, and instead created the webcomic The Kingdom of the Gods alongside illustrator Yang Kyung-il in 2014.

The series' portrayal of political dynamics of corruption and power highlights the disparity of growing concerns against the bourgeoise, suffering in the midst of a plague.

Speaking on the conceptualization of the plague, the creator argued its role in the narrative is to serve as a reflection of the corruption, greed, inequity and injustice committed by the ruling class, using it as a camouflage to usurp the political power to maintain influence in the Kingdom of Joseon.

Whilst the creator began to delve into the idea through the creation of Ashin's character when writing the second season, Kim Eun-hee wanted to further examine the collective trauma, grief and resentment born from the experiences of tragedy in the special episode.

[55] After the announcement for the special episode, it was confirmed that Jun Ji-hyun and Park Byung-eun would reprise their respective roles in Kingdom: Ashin of the North.

[56] Prior to the premiere of the second season, Joo Ji-hoon stated in a Forbes interview, that he signed on to star in the series, due to his faith in the project.

The website's critical consensus reads, "An enthralling blend of blood, terror, and political intrigue, Kingdom is a refreshing addition to the zombie landscape.

Aloysius Low of CNET praised the cinematography of the first season, stating that "shots cleverly linger on certain scenes to draw out the impressive sets, while adeptly tracking the action during sword fights or zombie attacks.

"[62] Renaldo Matadeen from CBR mentioned in a positive review of the first season, that "Kingdom makes even bolder sociopolitical statements than The Walking Dead does.

Sure, the AMC series waxes on about class and elitism, but Kingdom wades deep into governance and the divide between the rulers and the suffering populace.

"[64] Joel Keller from News AU recommended the first season in their review of the series by stating that "Kingdom dares to show that zombies aren't just a 20th and 21st-century phenomenon, and we applaud that kind of creative storytelling.

[68] Jorge Loser from Espinof wrote that, "Kingdom avoids unnecessary fillers in the story, and leaves a consistency in its spine that makes it worthy.

"[69] Sol Harris from Starburst praised the second season, stating that it is "a true roller-coaster of a thrill-ride, balancing nail-biting zombie carnage with the sword-based military action of countless samurai movies with a handful of darkly comedic moments that would make Sam Raimi proud.

"[70] Kevin Lever of Tell-Tale TV gave the second season a very positive review, writing: "the most important thing about Kingdom remains absolutely, undeniably riveting.

"[71] Rafael Motamayor from GameSpot recommended the second season in his review by highlighting that, "Not to be outdone by Game of Thrones, Kingdom also serves as an intriguing courtroom thriller", further praising the narrative, by adding that it "doubles down on the viral aspect of the zombie outbreak, exploring its natural origin, how it spreads, and most frighteningly, how it evolves.