When actor Yoo Ah-in was first approached to star in the K-drama Hellbound, he knew immediately he wanted to take on the project.

The 35-year-old plays charismatic cult leader Jeong Jin-soo in the series by director Yeon Sang-ho (Train To Busan, 2016).

It takes a bleak look at the chaos that envelops South Korea after supernatural beings appear out of nowhere to condemn people to hell and brutally beat them to death. It is based on the Web comic of the same name Yeon created.

At a press conference that was live-streamed from South Korea, the Burning (2018) star says: "I've been in acting for maybe half of my life and there are some works that just really appeal to me."

Still, he played a little hard to get with Yeon. "I was, like, 'We got to talk about the numbers, you know, there are some conditions,'" he says with a laugh.

Yeon, 43, jokes: "I dreamt I got a call that said Ah-in would take on the role and then I woke up and realised it was a dream, and a lone tear rolled down my cheek.

"But after that, he really called me and agreed to the role."

The director managed to land all of his first-choice actors for the series.

Kim Hyun-joo (I Have A Lover, 2015 to 2016) recalls: "When I first got to know director Yeon, I thought he's someone who's a master at creating a universe. People who are so talented tend to be close-minded and adamant about their opinions. And the picture that comes up when you search his name online reinforced that image.

"But he's actually a very fun, very smart person and very open-minded creator."

The 44-year-old plays a lawyer who leads the opposition to The New Truth cult and its related violent extremist organisation, Arrowhead.

Meanwhile, Park Jeong-min (Deliver Us From Evil, 2020), who plays a producer at a broadcast station, was already a huge fan of Yeon's Web comic.

Park, 34, says his character was particularly special because he is an Everyman.

"Unlike Jin-soo, my character is just a common man who lives and works and has a family. He can be anyone. And when a member of his family becomes involved in these unfortunate events, he has no choice but to be drawn into what's happening."

Though the series gets dark with its themes of faith, sin and the ugliness of humanity, the atmosphere on set was light-hearted.

Yang Ik-june (Breathless, 2008) says Yeon played a big part by taking on the role of class clown and making his actors feel comfortable. The 46-year-old actor plays a police officer who is struggling to cope with the murder of his wife.

Won Jin-ah (Life, 2018), who plays Park's wife in the series, agrees. The 30-year-old star says: "It was only after we saw the results on the screen that we're reminded it's actually a very dark piece."

Hellbound needed extensive post-production for its scenes featuring the monstrous creatures from hell. While filming, the actors often had to imagine what they would look like.

Yang recalls: "The actors who were standing in did an amazing job with their expressions and movements. It helped me to immerse myself in the scene."

Hellbound was the first K-drama to be invited to the Toronto International Film Festival in September. And with viral hit Squid Game becoming Netflix's most-watched series, interest in K-dramas is at an all-time high globally.

Yang says: "South Korea has always made great films and series. But with platforms like Netflix, creators in South Korea could reap the benefits of scalability and, sometimes, budget and casting too."

Yoo adds that the global spotlight has been encouraging and empowering for him as an actor. And he hopes that his new work will have legs.

"Hellbound has a completely different look, feel and tone compared with other Netflix productions like Squid Game and My Name. I hope it will not just be a fad or instant sensation, but also a piece of work that will be loved for a very long time, something people will talk about and have a lot of different interpretations about."

• Hellbound is available on Netflix.