Grammy-winning rock quartet Tool established themselves as one of America's most enduring and unpredictable acts with their ever-evolving brand of muscular but mind-altering sonics, wry sense of humor, and 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 aesthetic of prog rock, alternating between long, detailed instrumental interludes and lyrical rants in their songs. Debuting in the early '90s with Undertow, they were initially lumped in with the nu-metal contemporaries of the time, which made them a hit on rock radio with their sophomore effort, 1996's Ænima. However, they would soon break away from those associations, evolving beyond the confines of traditional song structures and song lengths, crafting epics that often clocked in past the ten-minute mark on 2000s head-trips Lateralus and 10,000 Days. After a lengthy 13-year hiatus, they returned to the fold in 2019 with their fifth opus, the chart-topping, Grammy-nominated Fear Inoculum.