George Marino mastered the original release of Metallica's album commonly called The Black Album.
Mastering is the final technical stage that prepares a completed mix for distribution and helps create a consistent sound across an album. Marino received the original album's mastering credit after the recording, overdubbing, and mixing work had been completed.
His credit is distinct from those of producer Bob Rock and engineer Randy Staub. Rock guided the production and performances, Staub engineered the sessions, and Marino handled the final mastering of the 1991 release.
Later anniversary editions introduced additional mastering credits, which can cause confusion. The 2021 remaster was handled by Bob Ludwig, while the original 1991 issue retained Marino's mastering credit. Therefore, the correct answer depends on whether the question concerns the original release or a later remastered edition.