"Fallen Angel" is the last King Crimson recording to feature Robert Fripp playing acoustic guitar. On subsequent recordings, he has played only electric guitar.
The song began as part of an extended instrumental improvisational piece performed by the original 1972-74 King Crimson lineup with Jamie Muir and David Cross. A version of this early piece, also titled "Improv: Fallen Angel" can be heard on the King Crimson Collectors' Club release Live at the Zoom Club October 1972.
Robert Fripp wrote the music for this track; John Wetton and Richard Palmer-James came up with the lyrics. Wetton was the group's lead singer, and Palmer-James helped out with lyrics (he also worked on the Red track "Starless"). In our interview with Wetton, he said that Palmer-James had a knack for taking his disjointed ideas and turning them into a cohesive story, which is what happened on this track.