Metallica became known as The Black Album because of its original cover design.
The album’s official title is Metallica, but its cover is overwhelmingly black and carries a barely visible embossed Metallica logo and coiled snake. The understated presentation made the informal nickname natural among fans and critics, even though the words The Black Album do not appear as the official title.
The cover was also connected to the album’s music. The snake was derived from the Gadsden flag, whose motto is Don’t Tread on Me; that phrase is the title of the album’s sixth track. The visual and lyrical references therefore reinforce one another.
Another source of confusion is Spinal Tap’s fictional album Smell the Glove, which is also associated with an all-black cover in the comedy film This Is Spinal Tap. Metallica jokingly acknowledged the resemblance in A Year and a Half in the Life of Metallica. Nevertheless, the nickname for Metallica’s 1991 record comes from its own cover presentation.