Brutally heavy but surprisingly catchy, metalcore band Atreyu first came together in California in the late '90s. From the very beginning, their sound was hard to pin down, mixing the angular rhythms of post-hardcore, the roaring riffs of extreme metal, and the howling vocals of screamo. Despite their ultra-aggressive style, Atreyu managed to seamlessly blend melodic hooks into their raging anthems, and they helped to bring metalcore to the masses in the '00s.