In April 1965, the song "Gloria" was released by Van Morrison's band, Them, through Decca Records. It was the first single taken from the group's debut album The Angry Young Them.

The track had already been issued as the B-Side to "Baby, Please Don't Go" a year earlier but obviously the record company thought there was more mileage to be had, so they re-packaged "Gloria" and shipped it again, only this time as an A-Side single. The studio version finds "Gloria" in its most condensed form, no doubt for radio-play purposes. Live renditions were another story altogether. Often Morrison would ad-lib entire sections on stage, stretching the song out to over 20 minutes. Both Patti Smith and The Doors' Jim Morrison later adopted similar approaches to the song, creating their own odyssey-length live versions.

Throughout June 1966, The Doors opened shows for Them at the Whiskey a-Go Go in Los Angeles. On the final night, Jim Morrison joined Them on stage to perform "Gloria", and during the 20 minute version the two Morrison men reportedly exchanged verses back and forth. There is no known recording of the show but there is a photo.

Live improvisation was a Jim Morrison staple throughout his short career. He regularly turned (already long) songs like "The End" and "When The Music's Over (Turn Out The Lights)" into sprawling, unpredictable jams that lasted for nearly half the band's set time. It seems likely that at least some of his inspiration for doing so stemmed from watching Van Morrison improvise verses during "Gloria" in '66.

Since its release, "Gloria" has been covered far and wide. In 1965 alone The Gants, The Bobby Fuller Four, and The Shadows of Knight all released "Gloria" as a single.