Now found in more places than the music store.

"Steve's dead now. From here on in, Steve's death will be represented by the oboe."
Tom Servo, Mystery Science Theater 3000 episode #209, The Hellcats

A leitmotif (pronounced "Light-motif") is a recurring piece of music (or at least melody) that represents a character, action, or theme. This is a well-established technique used in almost every medium that involves music and story. The leitmotif technique was invented (or at least codified) by opera composer Richard Wagner in the second half of the 19th Century. In his later operas, not only would every character have his/her own musical theme, but so did many objects, places, and even abstract ideas.

Leitmotifs are often named simply "<character>'s Theme" or "<noun> Motif."note  They often make up the bulk of movie and anime soundtracks, and a fair chunk of video game soundtracks as well.

This is different from an Image Song in that Image Songs exist only outside of the scope of the show that produced them. Compare with "I Am" Song.

If a character with a distinctive-sounding Leitmotif is in a production or episode with No Fourth Wall (or at least some Medium Awareness), one of his or her fellows may make a comment on how loud and annoying their theme music is. (To which the character will almost always reply, "What theme music?") Can become a Musical Spoiler for audiences if (or after) they recognize the theme. The character might also have their leitmotif as their own ringtone, for a subtler joke; see also Left the Background Music On.

Note that if a character's leitmotif starts playing during an action scene, start running.

Can become a Recurring Riff when used throughout a long-running series. Bootstrapped Leitmotif is such a variation, where a song that wasn't originally intended as a Leitmotif later becomes one.

One especially common leitmotif in video games is the Battle Theme Music, associated with monster battles in general. (Which also happen a lot.) If a specific character's Battle Theme Music is actually a remix of their Leitmotif, it may be a Boss Remix.

See also Mood Motif, Standard Snippet. Supertrope to Love Theme.