Bob Rock was the outside producer who worked with Metallica on the 1991 album Metallica, commonly called The Black Album.
The band had been impressed by Rock's production of Mötley Crüe's Dr. Feelgood and hired him for the next Metallica project. His approach encouraged the musicians to record more collaboratively and helped shape the album's powerful, polished sound.
Rock's involvement was not always easy. The sessions became known for arguments and demanding retakes, as he pushed the band to improve performances, lyrics, vocal arrangements, and the live feel of the recordings.
Metallica members James Hetfield and Lars Ulrich also received production credit. Bob Rock nevertheless remains the album's principal credited producer and became a long-term collaborator with the band.