Metallica is one of the most influential thrash metal bands since its start in 1981. Understanding the background of the band is essential to growing an appreciation for the music. Above all, one theme which has been prominent throughout the songs is the trials of mental and physical struggle in one’s life. Undoubtedly, the themes have been constant, but the music and sound of Metallica have been evolving as the band developed who they were and whom they wanted to be. These songs have developed recognizable musical elements that became the essence of Metallica and their pieces.​