Mastodon guitarist Brent Hinds wasn't always on the highway to hell. For most of his childhood, Hinds went to Christian school and attended church every Sunday with his parents and older brother. Then he discovered rock 'n' roll, started playing guitar, picked up a copy of Anton LaVey's The Satanic Bible, and finally shed his remaining Christian vestiges with two tattoos: one of Jesus holding a black sheep on his left forearm, one of the devil on his right.

"It's from the [AC/DC] song 'Hell's Bells," Hinds explains. "That line that goes, 'If God's on the left then I'm sticking to the right.'"

These days, Hinds is a PTA mom's nightmare, drinking, drugging, fighting, fucking, and playing in numerous bands, including the mighty Mastodon, one of the most successful and hardest working prog-metal outfits. He's also added significantly to his tattoo collection, leaving just one thigh and "both butt cheeks" to have inked when he's older. Hyperkinetic drummer and lyricist Brann Dailor and talkative, technically gifted guitarist Bill Kelliher are similarly decorated. Only easygoing vocalist and bassist Troy Sanders is relatively ink-free, with just a few small pieces on his legs.

Collectively, most of Mastodon's tattoos are playful or cool in a nerdy way. There are a slew of tattoos from the Star Wars saga (a must for prog geeks of all stripes), a zombie family, a sexy Ms. Pac-Man adorned in stockings and a garter belt, a giant yeti, a "Mastodragon," and John Travolta from Saturday Night Fever.

Some of the tattoos are far more meaningful. Sanders had his daughter's name tattooed above his right ankle when she was born, and when she turned 5, her handprint was inked on the outside of one leg. Last year, when Hinds's dog of 16 years died, he had "R.I.P. Melvin" tattooed on his forearm. And, most significantly, in 1995 Dailor had a sacred heart inscribed with his late sister's name, Skye, and the dates 1976–1990 on his chest, with flames going up his throat. "That's my area for her," he says in a soft, somber voice. "I surrounded it with yellow roses because she loved those."

Before last year, Dailor had never really spoken about his younger sister, who committed suicide following a long bout of depression. But as Mastodon started working on their fourth full-length album, Crack the Skye, the drummer decided it was time to reference that dark part of his life in the new record title and lyrics. "I guess it was therapeutic. I'm still not 100 percent sure," he says. "There are definitely things on this album about that, and I think I'll just keep writing about it. That's gonna have to be the way I deal with it for a while."

Crack the Skye is easily Mastodon's deepest, most personal album, yet it's hardly morose, and if Dailor hadn't revealed anything about his past, there'd be no way of knowing he was carrying such heavy personal baggage. Such is the way of the Mastodon. Since forming in 2000, the Atlanta band has confronted heartache, pain and hardship through metaphor and escapism. The group's music—a complex, riff-heavy mélange of heavy metal and prog rock—requires focused concentration. You can't casually listen to Mastodon. You have to clear your mind and inebriate yourself in the details. Like Tool and Neurosis, Mastodon are aggressive, cerebral and innovative. Many of their songs have choruses, but you have to wade through two verses, a pre-chorus and a middle-eight to get there. Some tracks don't have choruses at all, just rhythm shifts and unconventional time signatures.

"I usually say I don't write songs anymore, I write many songs within one song," says Hinds, the most attention-deprived member. "As a fan of music, I get bored with pauses. I'm a big Frank Zappa fan—I wanna hear the whole entire orchestra of sound onslaught at once."