Metallica's 1991 self-titled album, known as The Black Album, is the band's fifth studio album.
It followed Kill 'Em All from 1983, Ride the Lightning from 1984, Master of Puppets from 1986, and ...And Justice for All from 1988. Those four preceding records established Metallica as one of the leading bands in thrash metal.
The fifth album represented a deliberate broadening of the band's musical approach. Songs such as Enter Sandman, The Unforgiven, and Nothing Else Matters used more accessible structures without abandoning heavy guitars or Metallica's identity.
Some listeners call it the band's first mainstream album, but that wording can be misleading: Metallica had already achieved major success before 1991. The Black Album was instead the breakthrough that expanded their audience dramatically. It became the group's first album to reach number one on the Billboard 200 and remains their best-selling studio release.