(Book). Metallica, the seventh-biggest recording act in American history, are consummate musicians but it wasn't always that way. A significant proportion of their playing expertise was acquired from a pivotal three-year period in their history 1983 to 1986 during which their music, a potent variant of thrash metal, evolved from garage-level to sophisticated, progressive heights thanks to the teachings of their bass player, Cliff Burton. The San Francisco-raised Burton pushed the band to new musical levels with his musical training, songwriting ability, and phenomenal bass guitar skills. Cliff's life was short but influential; his death was sudden and shocking. With his death, Metallica's most critically acclaimed period of activity ended. They went on to record huge-selling albums, but by their own admission, never pushed the creative envelope as radically as they had done in the first four years of their career.