Bong Joon Ho at the Walter Reade Theater Thursday night.

Snowpiercer director Bong Joon Ho had initially envisioned the role of Mason as a middle-aged man, but that all changed after he met Tilda Swinton. The Korean filmmaker visited the Film Society of Lincoln Center Thursday night for an extended Q&A after a special screening of his sci-fi drama at the Walter Reade Theater. Snowpiercer features a cast from Europe, North America, and Asia and was filmed primarily in the Czech Republic.

In 2011, Bong served on a jury at the Cannes Film Festival where he met Swinton who was attending the annual May event with her lauded We Need to Talk About Kevin, which premiered in competition that year. Their meeting lead to the Oscar-winning actress joining the cast of the film, which will open theatrically in the U.S. this weekend at the Film Society.

“We had breakfast together and I said, ‘I’m a fan,’ and she said, ‘I’m your fan too, I loved The Host. Let’s do something together,'” Bong recalled through a translator at Walter Reade to a packed house. “And then when I got back and looked at the script, I saw there was nothing for her to do, so I wasn’t sure what to do. But the character of Mason was originally meant for a middle-aged man and I thought, ‘That would be good for Tilda,’ so I just changed it from a man to a woman.” John Hurt was also an early cast member to join the production, along with Song Kang-ho and Ko Ah-sung, both of whom had starred in Bong’s 2006 feature, The Host.

“[John Hurt and I] met for coffee in London and at the time I only had concept art and showed it to him and he loved it,” said Bong. “Of course [he and Swinton] are very respected actors so having them on board made the rest of the acting process much easier.” Chris Evans, Ed Harris, Jamie Bell, Octavia Spencer, Ewen Bremmer, Steve Park, and Alison Pill also star.

Set in the future, Snowpiercer revolves around a time when a failed global-warming experiment kills off all life on the planet except for a lucky few that boarded the Snowpiercer, a train that travels around the globe, where a class system evolves. Passengers in the front of the train bask in a luxurious, privileged quarters, while the back of the train is quite the opposite.

“After showing the movie in Korea, one person tweeted that when he was going home he kept moving his way to the front of the subway,” joked Bong.

Bong happened upon Snowpiercer while visiting his favorite comic book shop in Seoul. The French comic book Le Transperceneige was among the purchases he made that day in the mid-2000s and he quickly realized that he wanted to make it into a film.

“I’m an avid graphic novel collector,” said Bong. “In France it wasn’t that famous. It won some prizes, but it was nothing as big as Tintin. It was only published outside of France in Korea. I read it in 2005 and as I was walking out of the store, I thought, ‘I have to make this film.’ At the time, I was in pre-production for The Host.

[Snowpiercer opens at the Film Society of Lincoln Center this weekend with Bong attending select post-screening Q&As.]