Metallica first reached number one on the US Billboard 200 with its 1991 album, commonly called The Black Album.
The record debuted at number one on the Billboard 200 and remained at the top for four consecutive weeks. This was a major milestone because it was Metallica’s first album to lead the US album chart.
The album’s performance reflected both its huge first-week audience and its unusually long commercial life. It sold 598,000 copies in its first week in the United States, was certified platinum within two weeks, and continued returning to the Billboard 200 long after its initial release.
The Billboard 200 is an album chart, not a singles chart. Metallica’s songs also appeared on the Billboard Hot 100 and rock charts, but those measure individual tracks or radio performance. The chart achievement in this question refers specifically to the album’s overall US ranking.