Tool established themselves as one of America's most enduring and unpredictable acts with an ever-evolving brand of muscular but mind-altering sonics, a wry sense of humour, and a mystical aesthetic that attracted a cult-like following of devoted fans with just a handful of albums spread across decades. Their greatest breakthrough was to meld dark underground metal with the ambition of art rock, crafting multi-sectioned, layered songs as if they were classical composers. While embracing the artsy, they also paid musical homage to the relentlessly bleak visions of grindcore, death metal, and thrash. Even with their post-punk influences, they executed their music with the sound and feel of prog rock, alternating between long, detailed instrumental interludes and lyrical rants in their songs.