Bob Rock produced Metallica's 1991 album Metallica, commonly known as The Black Album.
Rock had impressed the band with his work on Mötley Crüe's Dr. Feelgood, released in 1989. His approach helped Metallica pursue a more polished, heavier, and more accessible sound than on its earlier thrash-oriented records.
The sessions were demanding. Rock encouraged the musicians to record collaboratively as a band and pushed James Hetfield to develop stronger lyrics and vocal performances. The producer and group argued frequently during the process, and Rock later described the experience as unusually difficult. Despite the tension, the album became Metallica's commercial breakthrough and one of the most successful heavy-metal albums ever released.