"Who Killed Marilyn?" is a song by Glenn Danzig, about questions surrounding the death of actress Marilyn Monroe, with the titular question suggesting she was murdered. Though Danzig's first solo single, the song has since been included on various collections by Danzig's group The Misfits.

The B-side, "Spook City USA" was also recorded previously with the Misfits during the Night of the Living Dead session, but that much faster version was not released until the 1996 release of The Misfits Box Set. There is some dispute as to the performer credits of "Who Killed Marilyn?" and the reasons for recording and releasing it in the first place. Misfitscentral.com lists Glenn Danzig as playing drums, bass, guitar, keyboards and all vocals. Yet Danzig's erstwhile bandmate, bassist Jerry Only claims in Ugly Things #12 that the song was recorded by Danzig and "the guy across the street from us." Danzig claims that he and Misfits drummer Googy couldn't get Jerry and guitarist Doyle to practice and perform more often, and "Who Killed Marilyn?" fulfilled Danzig's need to perform and release his songs on a more regular basis. Jerry claims he had no reason not to do the songs and doesn't know why Danzig released a solo single.

Whatever the history behind the songs, "Who Killed Marilyn?" continued Danzig's obsession with the darker underside of American pop culture, as seen from the very first single's "She" (about Patty Hearst) to such songs as Violent World and American Nightmare. Other versions of this song have been released by the Misfts (Legacy of Brutality, the Boxset, etc), but the Glenn Danzig version recorded on this 45, along with the B-side, Spook City USA, are only available on this 45 and have never been released on CD.