Bob Rock was the producer who first worked with Metallica on the album commonly called The Black Album.
The project marked Rock's first production collaboration with Metallica. His approach encouraged the musicians to record more as a unit, rather than constructing many rhythm parts separately, and he placed greater emphasis on the bass sound and the overall live feel.
Rock is credited alongside James Hetfield and Lars Ulrich as a producer on the album. That shared credit can cause confusion, but Bob Rock is the distinctive answer because he was the outside producer brought in for the sessions and became central to the record's revised sound.