This is the 21st post in a weekly, yearlong series. Read about it here and see the list of previous songs here. A new post about a different song will be posted each Monday throughout 2016. You can listen to the songs in a Spotify playlist.

By the time John Williams composed the score for the movie “Star Wars,” which came out 39 years ago this week, he had already scored several TV shows and movies, including “Valley of the Dolls,” “Goodbye, Mr. Chips,” “Fiddler on the Roof,” “The Poseidon Adventure” and “Jaws.”

So by no means was the soundtrack from a long time ago in a galaxy far, far away Williams’ breakthrough hit. But of all the iconic film scores he’s produced, which are among the most iconic in cinematic history, it is the music from “Star Wars” that is Williams’ most beloved and recognized. When the man dies, and we pray he will outlive Master Yoda, it is “Star Wars” that will lead his obituary, mentioned before “Indiana Jones,” “Superman,” “Jaws,” “Jurassic Park,” “E.T. the Extra-Terrestrial,” and the “Harry Potter” movies.

While Williams’ most familiar style has the orchestral hallmarks Tchaikovsky or Richard Wagner, his background gave him fluency in a wide range musical styles. After a stint in the Air Force, Williams went to New York to attend the Juilliard School of Music. While there, he worked as a jazz pianist, both in clubs and on recordings. After moving to Los Angeles, he worked with Henry Mancini as a session musician on the “Peter Gunn” soundtrack.

These various gigs help explain why in just the “Star Wars” series alone, Williams’ work has enough nuance and variety that it’s hard to believe it all came from one composer. There is the grand symphonic main title, of course, but additionally there are orchestral string pieces, marches, and even songs written in languages specific to George Lucas’ “Star Wars” universe.

And then there’s the aptly named “Cantina Band,” a jazz-tinged song that was played in the first “Star Wars” movie, the film that is now referred to as “Episode IV” or “A New Hope.” In terms of iconic songs from the “Star Wars” series, it is tied with the main theme, “Imperial March,” and the “Force Theme.” The song served as the background music for the Mos Eisley Cantina, the intergalactic watering hole where Obi-Wan Kenobi (Alec Guiness) and Luke Skywalker (Mark Hamill) meet space pilots Han Solo (Harrison Ford) and Chewbacca (the big hairy dude, played by Peter Mayhew).

Williams wrote the song after Lucas gave him the directive to “imagine several creatures in a future century finding some 1930s Benny Goodman swing band music in a time capsule or under a rock someplace… how they might attempt to interpret it?” According to CBC/Radio-Canada, Williams recorded the song with nine jazz musicians, including a trumpet, saxophones, a clarinet, a Fender Rhodes piano, a Caribbean steel drum, another drum, an ARP synthesizer for the bass and various other percussion. The bottom end of the sound was minimized, with added reverb working to thin the instruments. The resulting track has been compared by some to Goodman’s “Sing Sing Sing,” which was the actual song that was played on set while filming the scene so that the actors playing the band members could dance to the tempo.

Like just about every aspect of “Star Wars,” everything has a backstory, including the band that performed the song. On the various soundtracks, the song is just referred to as “Cantina Band” and the other song in the Cantina scene is just called “Cantina Band #2.” But within the “Star Wars” universe, the “Cantina Band” song is called “Mad About Me” and the band of hairless, domeheaded aliens who play the song is called Figrin D’an and the Modal Nodes. They are of an alien race called Biths. None of this comes from the movies, though; the band’s backstory is fleshed out in “We Don’t Do Weddings: The Band’s Tale,” a short story by Kathy Tyers featured in the 1995 anthology “Tales from the Mos Eisley Cantina.”

“Cantina Band” — or “Mad About Me,” if you insist — had no words, and a rather simple melody. But for being just a background song that has zero effect on the plot, it has become one of the more frequently referenced and parodied parts of the entire “Star Wars” series. As such, there are more than two dozen covers, in a variety of styles. Not all of these are on YouTube, but they are on our Spotify playlist.

In the first two days that the original “Star Wars” was in theaters, musician and producer Meco managed to see the movie at least four times. Meco then pitched the idea of a disco version of the movie’s score to Casablanca Records, but the company didn’t move forward with the idea until company head Neil Bogart got to t finally see the movie. Meco’s “Star Wars Theme/Cantina Band,” a disco mashup cover of the two tracks, appeared on “Star Wars and Other Galactic Funk.” It was the most notable track of Meco’s music career, though he had arranged the horn section on Tommy James’ “Crystal Blue Persuasion” and later played a trombone solo on Diana Ross’ “I’m Coming Out.”

The 1995 album “Zum Teufel, Baby” by rock/parody band Nylon 66’ers was all over the map, combining elements of surf rock, pop, and oddly enough, Euro House music. As such, the band’s version of “Cantina Band” sounded like a mix of drums you’d hear at a punk show, accordions you might hear at a VFW hall, and 8-bit boops you’d hear at an arcade.

Northern Irish alternative band Ash covered “Cantina Band” as the B-side to the single “Girl from Mars” on its 1995 album, “1977.” The version combined surf style riffs, punk guitar licks, and samples of space battles that sounded plucked from video games. But unlike the aforementioned Nylon 66’ers version, the Ash cover of “Cantina Band” sounded less experimental, though that Ash version was weird, too.

Jazz band The Dixiedelics included “Cantina Band” on its 2011 album, “Live At Steamers.” The live version had the familiar instruments of a jazz band: clarinet, sax, trombone, tuba, piano, and drums. Those you’d expect, but it also had a banjo that, as subtle as it was, gave it a Dixie feel. Toward the end, the band deviated to a portion of the “Force Theme.”

The Saltine Ramblers drew upon influences that ranged from Cajun to bluegrass to folk and alt-country. The band’s version of “Cantina Band” began with a funereal-sounding 20 seconds of the “Force Theme” before going into the actual “Cantina Band” song. The textured instrumentation had as much of a polka sound as it did folky bluegrass.

The album “Uklele Foce Aloha Na Mezame,” or “Ukulele Force Aloha Awakenings” in some releases, featured Hawaiian-style ukulele covers of themes from the “Star Wars” movies. The collection was so exhaustive that it even included a ukulele version of the iconic “20th Century Fox Fanfare.” Hiroyuki Tominaga’s take on “Cantina Band” sounded familiar, but the ukulele gave it such a soft sound that it almost felt like a lullaby.

UK Klezmer sextet Klezmer Kollectiv did a stylized version for its album, “The Terk In America.” Despite the opening few seconds of the song, the rest of the track sounded similar to the original, albeit with certain instruments — the low horns particularly — sounding much noticeable.

Pianist Tom Ameen released an album of piano arrangements based on the scores from the “Star Wars” series. “Journey to the Stars” featured two versions of “Cantina Band.” The first was a straight-forward piano rendition, which sounded pleasant, but sounded like what you’d expect “Cantina Band” to sound like on a piano. But Ameen’s second version, in the style of a waltz, was slow and somber. By changing the pacing, Ameen transformed “Cantina Band” from space jazz into a sad and melancholy song that belonged in a period piece about Victorian-era orphanages or something equally sad.

The Central Band of the Royal British Legion included a big band version of “Cantina Band” on its album, “The Shadow of Your Smile.” This version sounded closer to Benny Goodman than the original “Cantina Band,” in part because The Central Band of the Royal British Legion wasn’t trying to sound like an band of space aliens. The horn sections sounded crisper and fuller, like the big band productions of the 1940s.

Boasting that it’s “the world’s only spooky/sci fi/punk rock lounge act,” The Jimmy Psycho Experiment covers movie themes, rock, and punk, all in an instrumental lounge style, and all the while wearing alien masks. Its album “Intergalactic Playboy” included covers of “Rocket Man,” “Space Oddity,” the theme from “Star Trek,” and the “Love Theme” from “Blade Runner.” The band’s take on “Cantina Band” was almost exclusively done with percussion instruments, save for a organ-sounding keyboard interlude in the middle that was reminiscent of the underwater levels of “Super Mario Bros.”

On the topic of video games such as “Super Mario Bros.,” the group Music Legends has translated several soundtracks and film scores into 8 bit versions. The group’s “8 Bit Star Wars Episode IV: A New Hope” recreated Williams’ entire score and, like “Ukulele Force Aloha Awakenings,” even included a stylized version of “20th Century Fox Fanfare.” For a generation of nerd who grew up obsessed with “Star Wars” and Nintendo, this version of “Cantina Band” done in 8 bit is one of the most satisfying callbacks to our childhoods possible.

Guitarist Florian Haack has recorded metal versions of themes from video games, TV shows, and movies. His version of “Cantina Band” might be his most accessible track, because a lot of his covers are obscure themes from video games. As in, he has metal versions of the themes from specific levels in “Street Fighter 2,” “Sonic The Hedgehog 2” and “Final Fantasy VII.” The metal flavoring comes mainly from Haack’s ornate guitars, though the pounding drums didn’t hurt.

M.R.C. Max Rebo Crew remixed “Cantina Band” into foggy dubstep jam. Alternating between choppy and danceable, this layered version began with the identifiable riff before slowing down the song and inundating the track with bass. It doesn’t sound like anything that would go over well in the Mos Eisley Cantina, but would probably be a hit at an Ewok rave.

Mitchell Moffit and Gregory Brown, who run the YouTube channel AsapSCIENCE, recorded an a capella song in which Moffit and Brown took turns singing about physics, chemistry, biology and mathematics. Each field of study got its own verse that was sung to the tune of a specific theme from the “Star Wars” series. “Cantina Band” served as the backing melody for the ode to chemistry. Which begs the question: if an a capella group samples an instrumental track, is that just a sample or can it be a cover? Does adding words to the cover of an instrumental track take it away from cover territory? Either way, watch this and then try not to sing this to yourself over the next hour. Or year.

Of all the songs we have discussed in this series, this is the first instrumental song we’ve reviewed. And yet it is also one of the most covered songs we have discussed. And these covers above only scratch the surface. The glut of covers out there speaks not only to the enduring popularity of all things “Star Wars,” but also to the quality of Williams’ writing. Just as ABBA’s “Mamma Mia” could be translated into every genre, so could “Cantina Band,” because the core arrangement, however simple, was based on a catchy melody rather than on specific instruments.

We’ve looked at songs associated with and performed in movies, but “Cantina Band” stands out. There was a “Mamma Mia” long before the musical of the same name and “I Say A Little Prayer” had a rich 30-year history before the cast of “My Best Friend’s Wedding” introduced it to younger audiences. But “Cantina Band” owes its entire existence to a movie, and unlike the others. And “Cantina Band” might be the only song we’ve discussed that’s performed by aliens. I say “might be” and not “certainly” because the jury is still out on some of the artists we’ve reviewed.

You can listen to these songs and previously discussed cover songs in a Spotify playlist.