On casting Robert Downey Jr. in 4 Roles: "That was Park Chan-wook's idea early on. In the book, there are these sorts of male-white figures of the American establishment. They're all differentiated in the book, but he had the idea. What if we have one actor playing all the parts kind of like Peter Sellers in Dr. Strangelove and immediately we thought that's a great idea. Robert Downey Jr.'s characters represent academia, intelligence in the military, entertainment, and politics. Even if they have opposing political ideas on the surface, there's something at the root that is working together. It's a kind of deep-state metaphor and - I don't want to give away the ending of the series - but it comes together in a way that feeds into The Captain's character, too."
"Casting of The Captain (Hoa Xuande) was very hard because it's really all from his perspective. The whole thing is on his shoulders. He's in almost every scene. And when he isn't, it's from his point of view, so he's a spy, you know, so he's got to be able to have that poker face. He's got to be able...it can't be on the surface. He's got to have a certain amount of control. So we had to have someone who was very emotional, but at the same time had a lot of control, who was very agile in a way, like the narrative of the book is, who is able to quickly change modes and at the same time sort of evoke the protagonists of American 70s action films, except from a Vietnamese side.”