Metallica’s fifth studio album, self-titled album (commonly known as The Black Album) was released on August 12, 1991 by Elektra Records.

Metallica have sold “Black Album” more than 100 million records worldwide. With that album, they are the most successful band in metal history regarding album sales.

Black album is the best-selling album in the United States since Nielsen Music began tracking sales in 1991. It has sold 16.4 million copies. Metallica has never sold fewer than 1,000 copies in a week since its release.

Here’s 10 things you probably didn’t know about Metallica’s Black Album. Compiled by Revolver Mag and Rolling Stone.

10. The Black Album’s shorter, more streamlined songs were a reaction against …And Justice for All’s proggy excess

“​​​​​​To me, the …And Justice For All album sounds horrible, awful, can’t fucking stand it,” James Hetfield told Uncut bluntly in 2007. “That was our fancy stage, showing off too much. We knew we had to move on and the Black Album was the opposite. So when me and Lars got back together after a short break, I said, ‘We gotta really try and write some shorter, to-the-point songs.'”

Hetfield wasn’t alone in feeling like Metallica had gone too fall off the proggy deep end with Justice. “We realized that the general consensus was that songs were too fucking long,” Kirk Hammett revealed to Rolling Stone in 1991. “Everyone [in the crowd] would have these long faces, and I’d think, ‘Goddamn, they’re not enjoying it as much as we are … I remember getting offstage one night after playing ‘Justice’ and one of us saying, ‘Fuck, that’s the last time we ever play that fucking song!'”

9. Metallica picked Bob Rock to produce the record, despite not being big fans of the bands he’d previously worked with

The band’s decision to hire producer Bob Rock to helm Metallica was a controversial one, since the Canadian producer and engineer was best known at the time for his studio work with Mötley Crüe, Bon Jovi, Kingdom Come, the Cult and Loverboy, five bands with just about zero thrash cachet. But the members of Metallica were more interested in the way he’d made those bands sound, rather than the music those bands had made with him.

“With Bob, we wanted a good mix,” Ulrich told journalist Garry Sharpe-Young in an interview for 2007’s Metal: The Definitive Guide. “We wanted that big sound at the bottom end, and I don’t care if that song is on a Bon Jovi record, a Cult record or a Metallica record. The sound is the sound and we needed that.”

8. “Enter Sandman” was the very first thing the band wrote for the album

Hooky, sinister and hard-grooving, “Enter Sandman” perfectly encapsulated Metallica’s new direction. But rather than slowly transitioning towards a fresh approach, the band dove right in during the initial writing sessions for Metallica, taking a simple bluesy guitar lick from Hammett and quickly hammering it into what would become their biggest hit.

“‘Enter Sandman’ was the first thing we came up with when we sat down for the songwriting process in July 1990,” drummer Lars Ulrich recalled in 2014. “The 10-minute, fucking progressive, 12-tempo-changes side of Metallica had run its course after …And Justice For All. We wanted to streamline and simplify things. We wrote the song in a day or two. All the bits of ‘Enter Sandman’ are derived from the main riff.”

7. The guitar solo on “Enter Sandman” was inspired, in part, by a sample on an Ice-T album

“I think the time has come to reveal where I actually got the guitar lick before the breakdown in ‘Enter Sandman,’ Hammett told Guitar World. “It’s from ‘Magic Man,’ by Heart, but I didn’t get it from Heart’s version. I got it from a cut off Ice-T’s Power album, where he sampled it. I heard that and thought, I have to snake this!”

6. James Hetfield’s vocal performances on “The Unforgiven” and “Nothing Else Matters” were directly inspired by Chris Isaak

A huge international hit in late 1990 and early 1991, Chris Isaak’s “Wicked Game” also caught the ear of James Hetfield, who asked Bob Rock to help him emulate the singer’s moody vocals on two of Metallica’s slower tracks.

“He [Hetfield] said, ‘Bob, I’ve never really sang before – I’ve just kind yelled,’” Rock recalled in a 2015 interview with Chris Jericho. “He played me a Chris Isaak record, and he said, ‘On ‘Nothing Else Matters’ and ‘The Unforgiven,’ I want to sing. How do you sing like this?’ I said, ‘I’ll get you a great vocal sound, so you don’t have to double your vocals. What you hear in Chris Isaak’s voice is the nuances when he sings – he isn’t doubled. He’s actually performing. You perform.’ We set it up so he was comfortable and had a great vocal sound, and then he sang. Every day he got better, and he got comfortable with it. He became a great singer.”

5. Metallica and Bob Rock found working with each other so difficult that they planned to never do it again

If you’ve ever watched the incredible documentary A Year and a Half in the Life of Metallica, you know that the making of the Black Album was a tense, contentious affair. “I used to call James Dr. No,” Rock told Rolling Stone. “Whenever I was about to make a suggestion that seemed even a little off the wall, he’d say no before I’d even finished the first sentence.” Indeed, things were so tense during the recording sessions, that the producer “told the guys when we were done that I’d never work with them again. They felt the same way about me.” Of course, things worked out a little differently. After the album’s smash success, Rock and Metallica would go on to collaborate over three more albums, Load, Reload and St. Anger.

4. Kirk Hammett appears in the video for “Nothing Else Matters” – but he doesn’t actually play on the track

Originally written by James Hetfield as a love song to his then-girlfriend – and based around a musical figure that he discovered while absent-mindedly plucking his guitar strings during one of their phone conversations – “Nothing Else Matters” was a huge departure for Metallica. After hearing a rough version that Hetfield recorded for himself on a cassette tape, Ulrich convinced him that the band needed to record the song for Metallica; Hetfield then recorded the song’s acoustic intro and bluesy guitar solo himself, making it one of the few Metallica tracks that Kirk Hammett doesn’t play on.

“I had to relearn that whole intro part to play by myself onstage,” Hammett recalled in 2012, “which was a little bit intimidating for me at that point, [because] we never had a song that started that way.”

3. The album also marked the first time that Metallica had ever recorded their basic tracks “live” together in the studio

“We wanted a live feel [to the album],” James Hetfield told Guitar World in 1991. “In the past, Lars and I constructed the rhythm parts without Kirk and Jason, or Lars played to a click by himself. This time I wanted to try playing as a band unit in the studio. It lightens things up and you get more of a vibe. Everyone was in the same room and we were able to watch each other. That helped a lot, especially with some of the bass and lead stuff. It also helped that we’d played most of the songs for two months, even before we entered the studio.”

2. “Nothing Else Matters” was not intended to be a Metallica song or to be played for “other people”

“It was a song written in hotel rooms on [Justice] tour about missing friends at home, being out for such a long time,” Hetfield told Jeff Woods in 2016. “That was a song that was not meant to be played for other people, it was for me. I think that’s important — to write music that makes you feel good, I’ve got quite a few songs that are like that. ‘Nothing Else Matters’ was heard by the band, they thought it was amazing. I though, ‘You’re crazy. That’s just this sappy ballady thing that makes me feel OK.’ ‘No, that’s good!'”

That said, at least one other Metallica member was initially uncomfortable with the song, as well. “All I could think of at the time was, James wrote a fucking love song to his girlfriend?” Hammett said to Playboy in 2001. “That’s just weird.”

1. James Hetfield’s lyrics for “Enter Sandman” were originally about crib death

Though the music for “Enter Sandman” was the first thing the band wrote for Metallica, frontman and rhythm guitarist James Hetfield wouldn’t finish the song’s lyrics until much later. Originally envisioning the song as being about an infant mysteriously dying in its crib, Hetfield was asked by the band and their management – via producer Bob Rock – to tone down the lyrics.

“At first, based on the music and the riff, the band and their management thought it could be the first single,” Rock recalled in 2011. “Then they heard James’ lyrics and realized the song was about crib death. That didn’t go over so well. …

“I sat down with James and talked to him about his words,” Rock continued. “I told him, ‘What you have is great, but it can be better. Does it have to be so literal?’ Not that I was thinking about the single; I just wanted him to make the song great. It was a process, him learning to say what he wanted but in a more poetic and open sort of way. He rewrote some lyrics and it was all there … the first single.”