Even though Iron Maiden were on the brink of worldwide superstardom after their breakthrough sophomore effort, Killers, vocalist Paul Di'Anno left the band at the conclusion of their 1981 world tour. Many fans wondered if this would signal the end to one of metal's most promising new bands, but their worries were soon erased after hearing the 1982 masterpiece The Number of the Beast. Ex-Samson singer Bruce Dickinson replaced Di'Anno, and his strong, operatic vocals proved to be one of Maiden's most distinctive trademarks. And while the music on their first albums contained elements of punk, Beast was a 100 percent true heavy metal album, as Maiden's songwriting and sound continued to solidify. Topping the charts in the U.K., and becoming their first U.S. Top 40 record, The Number of the Beast spawned a pair of all-time classic metal anthems -- "Run to the Hills" (which dealt with the plight of the American Indian) and the demonic title track (which caused controversy among religious groups, who wrongfully labeled the band Satan worshippers). But, like its predecessor, not a single weak track is included -- "Invaders," "The Prisoner," "22 Acacia Avenue" (a follow-up to 1980's "Charlotte the Harlot"), and "Gangland" were all rocking highlights; the quieter "Children of the Damned" and "Hallowed Be Thy Name" were also featured. The Number of the Beast is quite simply one of the best heavy metal albums ever released.