Bob Rock was credited as the producer of Metallica's 1991 self-titled album.
The album marked Rock's first production work with Metallica. He had previously produced major rock and metal records, including albums by Bon Jovi and Mötley Crüe, and the band believed his experience could help them achieve a more powerful, polished sound.
Rock pushed Metallica to change its recording habits. Instead of constructing many rhythm parts separately, the musicians worked toward a more unified performance in the studio. His emphasis on bass presence, drum sound, and carefully shaped guitar layers became a defining feature of the album.
The production relationship was not effortless. Recording lasted roughly eight months, and the band reportedly clashed with Rock over performance and arrangement decisions. James Hetfield and Lars Ulrich also received assistant-production credits, but Bob Rock is the album's named producer. Flemming Rasmussen is often associated with Metallica's earlier albums, while Rick Rubin produced later Metallica projects, making both common mix-ups.