As the opening track on 1991's self-titled album, Metallica's 'Enter Sandman' is one of the most well-known songs from the band's last three decades. With a memorable opening guitar riff, the song lays the foundation for what fans affectionately call 'The Black Album.' Eventually, 'Enter Sandman' would turn into a staple at athletic events, including professional baseball games and wrestling matches.

Following the theme of a child dealing with nightmares, 'Enter Sandman' features one of the biggest highlights of any 'Tallica tune: a young child reciting 'Now I Lay Me Down to Sleep.' Why is this such a highlight? For one, the child's voice is that of Bob Rock's son, Rock being the producer behind 'The Black Album,' as well as 'Load,' 'ReLoad,' the first disc of 'Garage Inc.' and 'St. Anger.' But above that, the prayer gets an eerie treatment when frontman James Hetfield joins in with Rock's kid.

In a 2012 interview with Rolling Stone, drummer Lars Ulrich reflects on 'Enter Sandman' and its influence behind 'The Black Album.' "There was a riff on Kirk's riff tape," he explains. "The whole song is just that riff. 'Enter Sandman' was the blueprint. The rest of the record appeared over two months." In the 'Classic Series' documentary that covers 'The Black Album,' Kirk Hammett says of that riff, "I wrote it at three o'clock in the morning. I was all fired up."

In that same documentary, Hetfield listens to the song and calls it a "wall of guitars." He explains, "We couldn't just do one guitar for each guy. I had to do like three. It was a big wall of sound." That big wall of sound allowed Metallica to break into the world of rock radio, a world they previously had little experience in. 'Enter Sandman' introduced the band to a world of fans who never quite got into their four previous studio albums.

To date, Metallica have played 'Enter Sandman' more than 1,000 times in concert. The single was certified platinum on Dec. 14, 2009. As the chief curator for the Rock and Roll Hall of Fame, James Henke put together a list of the 500 songs that shaped rock and roll. 'Enter Sandman' was included on the unordered list (the only Metallica song on the list).

The demo of the song was recorded on Sept. 13, 1990. 'Enter Sandman' is one of four songs on 'The Black Album' that credits Hetfield, Ulrich and Hammett as writers.

Watch Metallica Perform 'Enter Sandman' - Moscow - Sept. 28, 1991