Subtitled "Carry My Joy on the Left, Carry My Pain on the Right," "Who Is It" was the lead single released off Björk's fifth studio album Medulla. It's one of the only songs on the album that's feasibly radio-friendly, with Medulla as a whole being one of the more experimental works from an experimental artist.
The song's chorus asks, "Who is it that never lets you down?" Björk has said that she wrote the song thinking about her conscience as the one who never let her down. Others have seen the song as being about motherhood or feminism.
"Who Is It" started with the title "Embrace Fortress." Björk wrote and recorded it with Polish American artist Bogdan Racynski for Vespertine, the album immediately preceding Medulla. In the end, Björk didn't feel like the song fit on Vespertine, which she considered "introverted and shy and not a very physical record." Raczynski claimed the song was withheld because it was it was so beautiful "it should be left in the clouds. People need mystery and romance."
Racynsnki must have jumped the gun on that conclusion because Rephlex Records released a limited vinyl edition of that original version in 2005.
As for Björk, she elected to include the song on Medulla, this time incorporating American beatboxer, rapper, and former member of the Roots, Rahzel Manely Brown, as well as Canadian Inuit throat-singer Tanya Tagaq. The electronic music duo known as Matmos provided "fruit-machine-noises" that can be heard in the choruses.
The song was one of Björk's more commercially successful singles, but it was even more beloved by critics. Most of the press for the song is enthusiastically laudatory.
The video for the song was every bit as distinct as the song itself. Shot in early September of 2004 in Hjörleifshöfoi, Iceland, it features Björk wearing a dress made out of metal balls molded into the shape of an enormous bell, and various other figures in outfits every bit as surreal. The dress, which was designed by Alexander McQueen, was sold for £44,000 in 2016 at the "Passion for Fashion" auction in London.
The version of the song used in the video omits Brown and Tagaq and adds a bell choir, per the dress.