Let’s define an “original theme song” as a piece of music that was specifically written to accompany and represent a particular work of art, such as a TV or radio program, a stage show, a movie, or a video game. (Or if not specifically written for that purpose, its first published use was for that purpose.) Works of art that consist entirely of music, such as an album of songs, are excluded. It’s not an original theme song if it was released as a single or album track first, and then only later appropriated for use in some other media!
Now, are there any original theme songs that became better known when repurposed as the theme song for an entirely different work of art?
For example, Henri Mancini wrote theme music to accompany the 1950s detective show Peter Gunn. However, to many of a younger generation, the music is much better known as the theme for the 1983 video game Spy Hunter. Now, I admit that this might not be the best example—I never saw the TV show myself, and I don’t really have a good grasp of the relative popularity of the show and the game. It could be that nowadays (or even back in the 1980s) most people who recognize the music still identify it with Peter Gunn rather than Spy Hunter.
Can anyone think of any better examples?