Enter Sandman was released in 1991 as the lead single from Metallica's self-titled album, often called The Black Album, and became one of the band's most recognisable songs. Its main riff, written by guitarist Kirk Hammett, helped bring heavy metal to a much wider mainstream audience. The track has since been used constantly at sporting events, in films and across online videos. Short clips of its intro and ending keep circulating on soundboards because the riff is instantly identifiable, even detached from the full song.