There’s little debate that “Enter Sandman” is not only one of the most popular songs in the Metallica catalog, but could be singlehandedly responsible for launching the metal titans into the mainstream. Yet while its simplistic opening riff and bedtime prayer breakdown are synonymous with the group, speculation has persisted over the years that their origins might not be as organic as fans have been led to believe.

The oft repeated story about the genesis of the primary hook to the track has Kirk Hammett coming up with it late one night while jamming at home in his bedroom. Later, when the guitarist brought it to the studio, Lars Ulrich proposed he duplicate the notes four more times. The Metallica drummer has said the entirety of “Enter Sandman” is based around that guitar riff which, iconic as it’s become, sounds quite a bit like another melody from a much lesser-known composition released more than two years prior.

Southern California crossover thrash outfit Excel came up in the mid-80s but never quite found widespread success. The group reached their apex with The Joke’s on You, an album released in June 1989 that featured the song “Tapping into the Emotional Void,” which – while not in the same key – has a main riff with an undeniable resemblance to “Enter Sandman.”

“You don’t know what to think,” Excel singer Dan Clements recalled of hearing the Metallica song for the first time during a conversation with the Los Angeles Times in late 1991. The newspaper reported the former band wouldn’t be filing a lawsuit over the musical parallels due to the all-consuming nature of such a legal maneuver. At that point, Excel had sold only 20,000 copies of The Joke's on You, compared to the three million units the Black Album, on which "Enter Sandman" appears, moved in just three months.

That same article saw a rebuttal from Metallica co-manager Cliff Burnstein, who claimed never to have heard “Tapping into the Emotional Void,” though he knew of Excel. Coincidentally, he and his partner at the management company Q Prime, Peter Mensch, were then managing the funk metal supergroup Infectious Grooves, whose lead guitarist Adam Siegel was a founding member of Excel. Interestingly enough, future Metallica bassist Robert Trujillo was also an original member of Infectious Grooves.

“If Excel could write that one (as good as that), I’m sure they can write more,” Burnstein said. “Then they’ll be successful.”

Though Excel never found fame, the big question, however, is whether Metallica – or Hammett in particular – were familiar with “Tapping into the Emotional Void.” Neither the guitarist nor the band has commented to date, but it should be noted that The Joke’s on You was released on Caroline Records. Back in the late '80s and early '90s, metal fans especially had a tendency to pick up an LP simply based on a label's track record.

Caroline had released out a few other titles that have tied directly into the fiber of Metallica's music, notably Mercyful Fate’s Melissa (1983), which features four of the five songs used in the medley named after the King Diamond led band on the Garage Inc. covers collection. The label also pressed the 1986 edition of the Misfits album Earth A.D./Wolfs Blood, known for the songs “Green Hell” and “Die, Die My Darling,” both of which Metallica have interpreted live and in the studio.

Not only is Dave Mustaine a longtime proponent of the theory that Excel inspired “Enter Sandman,” the Megadeth leader and onetime Metallica member has his own issues with the song. Less than a month before it was released at the end of July 1991 as a single by his former band, the soundtrack for the commercial flop Bill & Ted’s Bogus Journey landed on shelves and included the Megadeth track “Go to Hell.”

Like “Enter Sandman,” "Go to Hell" prominently features the phrase “Now I lay me down to sleep,” with the bedtime prayer heard at the beginning and end of the song, first recited by bassist Dave Ellefson’s wife Julie, and later by Mustaine. When the frontman heard the likenesses between the two pieces, he couldn’t help but be both unsettled and suspicious at what felt like another twist of the knife by Metallica.

“Granted, it’s not like I wrote the children’s prayer from which it was lifted (by both of us) …and maybe it was just pure coincidence. I have no way of proving otherwise,” he said in his 2010 memoir, Mustaine. "Both ‘Go to Hell’ and ‘Enter Sandman’ found their way into the public consciousness in the summer of 1991. I don’t know which song was written first. I don’t know if James [Hetfield] or Lars heard about ‘Go to Hell’ while they were in the recording studio. I just know that when I heard 'Enter Sandman,' I freaked out. The coincidence was mind-boggling and served as another reminder that I would never escape Metallica’s shadow. It would always be there, looming long and dark."

Whether it’s the case of two extraordinary chance occurrences or some underhanded, heavy metal skullduggery is something that’s probably moot at this point. “Tapping into the Emotional Void” and “Go to Hell” are mere footnotes of the genre, while “Enter Sandman” remains the second highest charting song in Metallica history – behind “Until It Sleeps” – and easily among the band's most recognized to the world at large.

Metallica Albums Ranked

There are moments of indecision when compiling this gallery of Metallica Albums, Ranked Worst to Best. After all, we really could have had – for the first time ever – a three-way tie for first.