Darth Vader’s theme is called the “Imperial March” and it does sound like a march. It’s the music played when he enters the movie or some scenes. It’s iconic and very well done – very recognizable.
It’s done in a minor key, giving it an ominous kind of feel. But, if you change the key to a major key, the “Imperial March” becomes a bit joyful. To me, it sounds like the theme to an 80s TV show or something at some points.
Yes, this is the same song – just in a major key instead of the original, minor key.