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
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