Although Metallica soon disavowed the term, this is the album that brought thrash metal to the forefront of hard rock -- both in terms of innovation and unbridled power. Yes, the riffs on songs such as "Disposable Heroes" and the jaw-dropping title song are faster than speeding bullets, but that's only half the story. In an era when most metal-mongers were satisfied with snickering about sexual conquests while recycling tired melodies, James Hetfield, Lars Ulrich, and company offered up provocative imagery -- like "Welcome Home (Sanitarium)," which is told from the point of view of an institutionalized inmate -- and remarkably intricate playing. Sadly, Master of Puppets also proved to be the final chapter in part one of Metallica's story, since bassist Cliff Burton was killed in a bus crash while on a European tour promoting the disc -- thus adding another level of meaning to "The Thing That Should Not Be."