Rivaled only by Black Sabbath and Judas Priest in regards to influence and impact on the early development of heavy metal, Iron Maiden took the style of heavy metal to a new and unique level. Developing among the New Wave Of British Heavy Metal, the band developed their own hybrid of heavy metal that introduced melodic guitar harmonies and chuggy base lines; more energy, more aggression, and more intricacy.Killers was Iron Maiden's first studio album but, depending on who you ask, isn't necessarily the best nor the most influential. Number of The Beast, even the title holds it's own hierarchy throughout the metal scene, and it's well deserved. Being the third album from the band, according to Bruce Dickinson "...[it] really set the scene for the albums that followed ... but of course, albums are not just about music, they're also a product of their times." This album transformed Iron Maiden's career. The album has a distinct remembrance about it, throughout it's entirety, which is a difficult thing to accomplish for an entire album.
Not that you should need more convincing, a strong line of metal bands throughout the era have covered Iron Maiden including Opeth, Cradle of Filth, Testament, and Lord Belial.