Bob Rock was credited as the main producer of Metallica’s 1991 album, The Black Album.
Rock had impressed Metallica through his production work on Mötley Crüe’s 1989 album Dr. Feelgood. The band hired him for the self-titled project, although the group initially had reservations about changing its established production team.
The recording process became famously demanding. Rock encouraged the members to work more collaboratively in the studio, record with a stronger live feel, and use harmonic vocals for James Hetfield. He also pushed for a more prominent bass sound than the one heard on ...And Justice for All.
Rock’s name is sometimes treated as the album’s only producer, but the formal credits also list James Hetfield, Lars Ulrich, and Metallica as producers. Bob Rock remains the central production figure associated with the album’s polished, heavy sound and with several later Metallica releases.