"The Call of Ktulu" is the Metallica's second instrumental.

The idea of the piece "The Call of Ktulu" 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 piece's name was taken from one of H.P. Lovecraft's main stories featuring Cthulhu, "The Call of Cthulhu", which was written in 1928. The name "Ktulu" is originally written "Cthulhu" by H.P. Lovecraft. In the story, it says that mentioning the name Cthulhu (Verbally or written) will bring him closer.