From the CD Ride The Lightning, the idea of the song is based upon H. P. Lovecraft's book The Shadow Over Innsmouth which was first introduced to the rest of the band by Cliff Burton. The song's name was taken from one of H.P. Lovecraft's main stories featuring Cthulhu, The Call of Cthulhu, which was written in 1928 for the magazine Weird Tales. It's also the last song to include songwriting credit for Dave Mustaine.