"Deirdre" is a song written by Bruce Johnston and Brian Wilson for American rock band The Beach Boys. It was released on their 1970 album Sunflower and subsequently as the B-side of the "Long Promised Road" single. The single never charted in the US or the UK. When asked about the song in 2013, Johnston elaborated:

I wrote all the music for the song and started writing the lyrics with Brian although that’s not his strong point, even though we must remember that Brian wrote all the lyrics for songs like "Surfer Girl" and "'Til I Die". So "Deirdre" was kind of my song and I split it 50/50 with him. It’s really about 99% my baby.

In 1977, Johnston rerecorded the song for his solo album Going Public.

The song was recorded on February 21 and March 21, 1969, at Gold Star Studios.

Rolling Stone said that song "could be Beach Boys-influenced anybody".

"Deirdre" was sampled for the 1994 video game EarthBound. A sample of the a capella intro of the song is arranged into the music for the Cave of the Past near the end of the game. This sample was in turn used in the 2015 video game Undertale as an instrument in the "Amalgam" battle music.

...
Wikipedia