John Williams composed "The Imperial March" from Star Wars as a military march because that's how Dart Vader enters a scene. The song is not only miitary, but downright evil. It's a tune that's been stuck in your head for almost 50 years now. Or at least in mine. But if you know a lot about music, you can do some odd things with a familiar theme.
Swedish guitarist Lucas Brar turned "The Imperial March" into a fugue, which is a composition with a main theme plus bells and whistles that complement and compete with the main theme, but always comes back to it. Read a better explanation here. Johann Sebastian Bach was well known for his musical fugues. Brar was thinking of Bach when he dressed up the march in a way that make it sound a little less ominous, or at least least a little less military, and a lot more interesting.
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