Last month, Jonathan Liu uploaded a YouTube video of his two-year-old daughter, Berry, freshly awoken from a nap, singing the Star Wars “Imperial March” to herself in her crib.

Berry had just had her first encounter with the original Star Wars trilogy. Her response to that particular tune was immediate. Liu also uploaded a video of Berry’s rendition of the Star Wars main theme, but this second video didn’t go nearly as viral. Obviously, there’s something irresistible about a toddler delighting in the forces of darkness.

If the gradual creep of John Williams’s 1975 theme for Jaws is the sound of lurking danger, his “Imperial March,” or Darth Vader theme, is the anthem of evil in full, glorious flight. The tune shares some of its doomy melodic DNA with the funeral march from “Chopin’s Piano Sonata No. 2”—that opening death knell in particular—but “The Imperial March” revels in a bombastic dastardliness all of its own, part-military, part-pantomime. In the concert arrangement, even the flutes in its middle section seem to quiver and fret all over the place while insistent blasts of brass loom overhead.

As a piece of music designed to menace and intimidate, there’s no beating it. It’s been widely deployed to galvanize sports fans and concert audiences, and enjoys long-held associations with such clear embodiments of evil as Mr. Burns, Dick Cheney, and this bird.

In the year that George Lucas cheerfully revealed his personal view that “sound” is more important in the Star Wars movies than dialogue, it’s worth contemplating the importance of Williams’s contribution to the saga, and why “The Imperial March” in particular can resonate so powerfully, even with those of us yet to be fully toilet trained.

During the mania surrounding Star Wars in 1977 it was, naturally, the main theme that underwent the bizarre disco treatment. The Meco track is still the top-selling instrumental single ever. But “The Imperial March”, with its hooky repetitions and heavy emphasis on the fascistic lockstep of its beat, was catchier and more on-point than any of Williams’s other themes to date; the galloping notes of his Raiders of the Lost Ark score was a year away. Even if it didn’t necessarily light up the dance floors, “The Imperial March” ruled the multiplex: at that point in the reign of the Hollywood blockbuster, it was Williams’s most irresistible earworm.

Looking at the numbers, it may seem like those watching The Empire Strikes Back are simply bludgeoned into submission. Replacing a far more brief and understated Imperial theme from A New Hope, some form of “The Imperial March” plays (according to the Rebel Force Radio: Oxygen podcast) 41 distinct times over the course of the second movie.

That might sound like an excessive bombardment, except for the variety of ways in which the theme is used. Its first occurrence in the movie, and in movie history, is almost subliminal: right after the introductory crawl, as the Imperial Destroyer dispatches its Probes, a lonely piccolo, buried in the mix, peeps out two measly bars of it. The theme makes its boisterous entrance proper just as we’re reintroduced to Darth Vader, surveying his fleet of Star Destroyers. Of course, it sounds out, after a tumble of timpani, in long seismic booms later in the movie, after Vader’s shocking revelation in the Reactor Shaft, the camera lingering on the wounded Luke as he “searches his feelings.” The first four notes crash down once more in the final moments of the end credits.

In the context of Williams’s banquet of musical ideas, it never feels like overkill; The Empire Strikes Back also offers up a magical theme for Yoda and a lush, romantic theme for Han and Leia, a tune that simultaneously updates the Princess’s own theme (intentional) and anticipates Marion’s theme from Raiders (probably not intentional).

“The Imperial March” even brings a sense of architectural unity to the maligned prequels: in The Phantom Menace, Williams embeds its most ominous twisting notes like a splinter in the oneiric innocence of “Anakin’s Theme.” By Revenge of the Sith, as darkness overtakes Anakin and Hayden Christensen becomes more insufferable, it has festered and grown into the theme we know. Whatever the gulf between the two trilogies, Williams’s organic musical storytelling remains remarkably cohesive throughout the saga. Even more surprising, then, that Lucas resisted the temptation to insert the theme into the remastered Episode IV in 1997.

With Star Wars, Williams was credited with pioneering the use of Wagnerian leitmotif in cinema: musical calling cards that reinforce the appearance of a character or idea. It’s easy to take for granted the ingenuity of applying a 19th-century operatic idiom to Lucas’s space fantasy, but it was exactly that kind of thinking that made the first movie work.

Composer Ennio Morricone criticized Williams’s “little marches” as insufficiently experimental (Morricone’s synthesized contrapuntal plinking for The Humanoid was his arty-farty take on what space ought to sound like), but the effectiveness of Williams’s score lies precisely in the way it made a far away galaxy feel closer to home. Even the diegetic music of the Mos Eisley Cantina sequence, where Williams had full license to get freaky—visually, it’s the highest concentration of otherworldly weirdness in Star Wars—was sensibly grounded in earthbound tradition. For all the kooky instrumentation of the infamous number (Trinidad steel drums and out-of-tune kazoos), Williams was intentionally evoking the very terrestrial swing stylings of Benny Goodman.

Apart from that, Williams drew on (less gracious commentators would say “ripped off”) classical music and old movie scores by Max Steiner and Erich Korngold: the Star Wars main theme owes a sizable debt to Korngold’s 1942 score for Kings Row. In the same way, Lucas drew on Flash Gordon and Kurosawa’s The Hidden Fortress. Aurally, the suns-scorched Tatooine desert took its cue from Stravinsky’s Rite of Spring; visually, the movie’s space battles were based on scenes from The Dam Busters and The Bridges of Toko-Ri.

Both Lucas and Williams credit their fundamental inspiration to an even more ancient and mystical source though: the collective unconscious. Star Wars was a retelling of the hero’s journey as explained in Joseph Campbell’s manifesto on mythology, The Hero with a Thousand Faces. (Roger Ebert put it another way: Lucas’s storytelling was “as deep and universal as storytelling itself.”) Williams, meanwhile, describes his music as “pre-language”, and his intentions to tap into “something earlier in the cultural salts of our brains, memories of lives lived in the past.” It’s significant that the only musical direction in Lucas’s Star Wars script, prior to Williams’s involvement, was to indicate that “War drums echo through the heavens” after the main title. In the history of music, what could be more primal than that?

Most tellingly of all perhaps, Williams’s initial concept of Star Wars was that it would be an enjoyable “light and sound show for young people.” The quote goes some way to illustrating his general approach, and maybe why a two-year-old can so thoroughly dig “The Imperial March.”

One of the more successful movie villain themes of the last year was Brian Tyler’s for Avengers: Age of Ultron, craftily employing an out-of-key piano and “wrong” notes played at the wrong time. However sophisticated the methodology, the result clearly isn’t as fun as “The Imperial March”. In fact, the Avengers movies employ leitmotivic scoring religiously—but when was the last time one of its heroes’ themes actually lodged in your memory?

Scoring The Force Awakens, as Williams told Vanity Fair earlier in the year, was like “adding paragraphs to a letter that’s been going on for a number of years.” Judging by what we know, and the sly presence of familiar themes in the final trailer (for which they were reengineered by John Samuel Hanson and Frederick Lloyd), it’s highly likely that Williams’s “Imperial March” is set to resume apace in one form or another. When it does, it will hark back to a bygone era of movie music, just as the first one did: a time when movie music set out to get a Force choke-like grip of its audience and not let go.

This story was originally published in Vanity Fair.