'Enter Sandman' was released as the lead single from Metallica's self-titled fifth album, commonly referred to as 'The Black Album', on July 29, 1991. This marked a significant turning point in Metallica's career, as the album represented a shift towards a more mainstream sound, blending heavy metal with hard rock elements. The song itself features a memorable, haunting guitar riff and a powerful, driving rhythm, characteristic of the band's earlier thrash metal roots but polished for broader appeal. The production, handled by Bob Rock, contributed to its radio-friendly sound while retaining the intensity that Metallica is known for. 'Enter Sandman' quickly became a commercial hit, reaching the top 20 in several countries and solidifying the band's status in the rock and metal scenes.
Thematically, 'Enter Sandman' delves into the fears and anxieties of childhood, exploring the unsettling feelings associated with nightmares and the loss of innocence. The lyrics present a narrative that evokes a sense of impending doom, as the protagonist is warned to "sleep with one eye open" and is haunted by the presence of the titular Sandman, a figure typically associated with sleep but reimagined here as a harbinger of nightmares. Lines like "Exit light, enter night" illustrate the transition from the safety of daylight to the dangers of the night, encapsulating the universal fear of what lurks in the dark. The song's juxtaposition of innocent lullabies with darker themes serves to amplify its emotional impact, making it relatable to listeners of all ages.