Who played bass on Metallica's 2003 album 'St. Anger'?

Bob Rock played bass on Metallica’s 2003 album St. Anger. Rock was primarily the album’s producer, but he also performed the bass parts during the recording sessions because Metallica had not yet formally replaced Jason Newsted with Robert Trujillo.

Jason Newsted had left Metallica in 2001, citing personal and creative pressures. Rather than immediately install a permanent bassist, the remaining members worked with Rock while making St. Anger. The album’s production was documented in the film Some Kind of Monster, which shows the band dealing with internal conflict, songwriting problems, and the search for a new bassist.

This question often produces confusion because Robert Trujillo joined Metallica before the album’s release and became the band’s permanent bassist in 2003. He therefore appears in the broader St. Anger era and promotional material, but he did not play the album’s recorded bass parts. Cliff Burton had died in 1986, and Jason Newsted was no longer a member when the sessions took place.

St. Anger was released on June 5, 2003. Its raw production, unusually prominent snare sound, and lack of conventional guitar solos made it one of Metallica’s most debated albums, while Rock’s temporary role remains a distinctive part of its recording history.