During the recording of "St. Anger" in 2003, Rock played a more hands-on role than ever before, even stepping in as the bassist for the album's recording sessions. This period was marked by tensions within the band, which were documented in the film "Some Kind of Monster". Rock's involvement during this challenging time helped Metallica navigate through personal and creative struggles.

Rock's first project with Metallica, "The Black Album", released in 1991, was a departure from the band's thrash metal roots, featuring a more polished sound with simpler arrangements. Rock's production emphasized clarity, dynamics, and accessibility, helping the album to become one of the best-selling records of all time.

Bob Rock's relationship with Metallica ended after "St. Anger", but his impact on the band's sound and success is undeniable. Under his guidance, Metallica explored new musical territories, resulting in a series of albums that expanded their fan base and solidified their status as one of the greatest rock bands in history.

Bob Rock's insistence on perfection and his meticulous approach to recording were initially met with resistance from the band. However, this rigorous process resulted in a refined sound that broadened Metallica's appeal. His influence was instrumental in crafting songs that balanced complexity with mainstream accessibility.