Without a doubt, Darth Vader, the lightsaber-wielding warlord dressed in black, is the most iconic character in the Star Wars films. Fans want to get as much of Vader as they can. The last time Vader was on the big screen was in 2005’s “Star Wars: Episode III-Revenge of the Sith.”

But the biggest revelation during this year’s Star Wars Celebration in London was that Vader would be appearing in the forthcoming “Rogue One: A Star Wars Story.” Director Gareth Edwards could not help but geek out over this development.

Edwards recalls that, in order to do a proper camera test, they had a superfan come on set with the world’s most detailed Darth Vader costume, complete with the voice box that made the distinctive breathing noises: “I knew he was coming, but I had forgotten about it. I got lost and I was walking through the corridor and then I heard the breathing. And I swear, I went from a 40-year-old to a 4-year-old walking up to him. Oh my god, it’s Darth Vader. You don’t want to talk to him, you don’t want to give him directions. I felt really embarrassed. And I looked at the rest of the crew, and they’re all standing around there like 4-year-olds.”

That was part of Edwards’ realization that Darth Vader was a learning process. It’s about more than just putting someone of the right height in the costume. “Firstly, the person playing him needs to have the right body language. You can’t teach it. You needed someone who had the right presence.”

Then, there’s the matter of getting the helmet right, as the helmet has gone through many subtle changes throughout the trilogies. “We put back all the imperfections and make it look like the ‘A New Hope’ Vader,” Edwards says. “If you don’t put the (actually makes the Vader breathing sound) in, it won’t work.” You have to have the right music. Vader needs to always have the highest eye lines, so you adjust the camera to make it so. “So there are strange things that only happen with Darth Vader, no one else.”

Then there’s the matter of that voice. Edwards likes telling the story of how James Earl Jones—the man who gave Vader his voice—came to record Vader’s lines for “Rogue One.” Edwards and the crew would be going crazy behind Jones’ back while the recording was going on.

That’s what it’s like working with Darth Vader, all secrecy and scariness. Felicity Jones is quite tight-lipped about her scenes with the Sith Lord, merely offering up: “He’s pretty frightening.”

Edwards says it’s all part of the job. “Psychologically, you have to park that, or you’ll get paralyzed. You get past that really quick. You start treating someone like they’re normal, and you realize you’re talking to Darth Vader. At one point, everybody has his own internal freak out.”