Metallica is one of the most important and most influential metal bands of all time, drafting the blueprint for thrash metal in their earliest days, then pushing the boundaries of mainstream metal and hard rock as they settled into their role as a popular legacy act as the decades went on. Between the meeting of raw energy and intricate speed metal compositions of their 1983 debut Kill 'Em All and the layered, radio-geared production of 1991's self-titled "black album," the band turned in classic album after classic album, each new chapter leading the development of metal on a global scale.