Bob Rock became for a short period a musician of Metallica, recording bass on all tracks of the St. Anger album (produced by him and Metallica), as former bassist Jason Newsted left the band and Robert Trujillo had not yet joined.

Bob Rock, born Robert Jens Rock, is a Canadian musician, sound engineer, and record producer. Though his initial career was as guitarist and bass player in minor bands (only a discrete success with the hit single "Dirty Water" of his Canadian band "Rock and Hyde"), Rock is best known as a producer for rock and heavy bands such as Metallica and Mötley Crüe. He also worked with Aerosmith, Bon Jovi, Cher, The Cult, David Lee Roth, Skid Row, Veruca Salt, Nina Gordon, The Offspring, 311, Our Lady Peace, The Tragically Hip, The Tea Party, Lostprophets, American Hi-Fi and Simple Plan.