Bob Rock played the recorded bass parts on Metallica’s 1991 album commonly called The Black Album.
Jason Newsted was Metallica’s bassist during the sessions and remained a full member of the band. However, disagreements about the bass arrangements led to Rock performing the bass parts heard on the finished album. Newsted’s role in the band and his role on this particular recording are therefore not identical.
This detail is often overlooked because Newsted appears in the album-era lineup and participated in the band’s work around the release. The album credits and recording history distinguish the live member lineup from the musicians who performed specific parts in the studio.
Rock was primarily known as the producer, making his bass contribution especially notable. The decision became part of the album’s complicated production story and is one reason questions about the record’s lineup can produce different answers depending on whether they concern membership or recorded performance.