They saved the best for last in the first official trailer for Rogue One: A Star Wars Story, released Thursday night. A blink-and-you'll-miss-it image of a reflective black helmet, seen from the back. And of course, the gas-mask sound of breathing.

One inhale was all it took.

Darth Vader, the most iconic cinematic villain of the 20th century, was on screen in a live action movie again -- for only the second time in the 21st. Despite the very strong possibility that his screen time in Rogue Onewill make Jared Leto's brief turn as the Joker in Suicide Squadlook like a leading role, Vader dominated the headlines and social media reactions.

Why is this? When just about every old-school science-fiction villain would seem at least faintly ridiculous if they returned these days -- think Ming the Merciless in Flash Gordonor Ricardo Montalban's bare-chested, long-haired appearance in Star Trek: Wrath of Khan-- why are we still so perversely fascinated by the guy in a breathing apparatus and motorcycle gloves?

Why is Darth Vader the bestselling Hasbro Star Wars action figure, year after year? Are we simply a culture of Kylo Rens, forever worshipping this long-dead grandfather?

The fact that we were taken with the Dark Lord of the Sith in the first place came as something of a surprise to George Lucas. Having just filmed the Vader scenes in Star Warsat Elstree in 1976, Lucas came back and lamented to the movie novelization's ghost writer, Alan Dean Foster, that Vader wasn't a scary villain at all and should probably be killed off in the follow-up novel.

If you find this hard to believe, consider the fact that Vader gets a mere 10 minutes of screen time in the original movie. He was the heavy, the muscle; he plays second fiddle to Governor Tarkin (Peter Cushing) throughout. The Vader costume cost less than $1,500 to put together. Cushing was paid twice that every day he was on the set.

And then there was the way Vader sounded on set, voiced in the provincial Southwest England accent of bodybuilder Dave Prowse, causing the British crew to call him "Darth Farmer" behind his back.

The alchemy that made Darth Vader what he is today all happened in post production. The menacing baritone of James Earl Jones played a huge role, of course. (Lucas was originally hesitant about how it would look if the only black actor involved in the production was voicing a villain; it took the urging of Godfather casting guru Fred Roos to persuade him to hire Jones anyway.)

But that wasn't the main thing. Consider the very first time we see Vader in Star Wars: he doesn't talk. He just enters the corridor of the Tantive IV blockade runner as his Stormtrooper legion snaps to attention, stares at the corpses of his rebel enemies for a few seconds, then stalks off screen.

And yet John Williams' score cuts out, for the first time in the movie, the second he appears. Why?

Answer: so we can hear the breathing. That horrifying, claustrophobic sound, the iron-lung-heavy breath we know so well, is in fact sound designer Ben Burtt wearing a scuba mask. Burtt told me he simply recorded a tape of himself inhaling and exhaling through the mask at three different speeds. That's all he used for the rest of the original trilogy.

Generally, you only get to hear the faster versions when Vader is lightsaber fighting -- which means it's the slow, relaxed version that terrifies us so much. (In yoga, they call this kind of oceanic inhalation and exhalation "ujjayi breathing"; many yoga teachers nowadays will describe it by simply telling you to "breathe like Darth Vader.")

The breath is what Vader gets in the first movie in lieu of a backstory. In fact, it's all you need to invest the character with weight and mystery. Immediately the audience understands there's a man trapped in there; Vader's no droid. He must have been horribly injured to be masked up like that. And away our minds go, inventing our own backstory.

Depending on what you think of the prequels, this may be better than the backstory we actually got. The mystery fires our imaginations more than seeing the whiny, creepy brat that Anakin Skywalker once was. It's telling that the most acclaimed prequel was Episode III, Revenge of the Sith, which features the moment when the gas mask and samurai helmet finally clamp into place.

It's also appropriate, if a little cheesy, that the scene references Frankenstein when Vader bursts out of his restraints. As a character, Vader is nothing if not a Frankenstein's monster. Part Skywalker, part machine. Little bits of Dave Prowse, James Earl Jones and Ben Burtt, not to mention legendary conceptual artist Ralph McQuarrie. He's a visual reference to World War II and also to the Kurosawa Samurai movies Lucas loved so much, topped off with the black cape of a super villain.

And like Frankenstein, Vader far surpassed what his creator expected. Rogue Onewill be the first movie in which he appears that doesn't have George Lucas' name in the director or producer role. (He's already shown up in the Disney XD cartoon Star Wars Rebels, which also precedes the timeline of the original movie).

No matter how much or little we see of him inRogue Onethis December, there's no doubt we will see those dead eyes and hear that scuba mask again -- and soon.