Bob Rock's 1989 album Dr. Feelgood impressed Metallica before The Black Album was recorded.
Rock produced Mötley Crüe's Dr. Feelgood, a commercially successful hard-rock album released in 1989. Metallica admired the record's production and decided that Rock could help them develop a fuller and more forceful sound for their next release. His hiring represented a deliberate move away from the production team associated with much of Metallica's earlier work.
Rock's role went beyond simply recording the band. He encouraged the members to play together in the studio, asked for more direct song structures, and insisted on repeated takes until the performances met his standards. He also helped bring Jason Newsted's bass forward in the mix.
The collaboration was difficult. Metallica and Rock argued regularly during the sessions, and Rock later described the experience as highly stressful. Nevertheless, the resulting album became a global success and established a production partnership that continued on later Metallica releases.