If you are a rap fan—and of course you are—you have likely already listened to metal. Maybe it was Slayer guitarist Kerry King's riffage on Licensed to Ill, or that punishing Slayer "Angel of Death" sample (Jeff Hanneman this time) on Public Enemy's "She Watch Channel Zero!?" or the Anthrax-fueled remake of PE's "Bring the Noise." Or maybe it was the Judgment Night soundtrack, which again featured Slayer—no surprise, since they were once signed to Def Jam and produced by Rick Rubin—this time teamed with Ice T, who has his own metal band, Body Count. Or maybe it was Nonphixion, whose "The CIA Is Still Trying to Kill Me" namedrops more metal acts than this piece will.

Rap and metal were both spawned on music's fringes, sharing everything from driving beats to PARENTAL ADVISORY stickers. And both have roots in strife, namely late '60s working-class England and late '70s inner-city New York. Much like rap too, metal has grown tremendously and has much greater depth than a cursory examination would reveal. A band like, say, Meshuggah, who rely on near mathematical precision, bear little similarity to a glammed-up Mötley Crüe or a truly evil Norwegian "band" like Burzum, yet they are all considered metal.

Fans of both rap and metal were on the fringes as well, although they started on opposite sides. Metal was decidedly white, rap decidedly not so much. The Levi's and leather jackets of metal fans were taboo to sportswear-obsessed rap fans. If they shared anything stylistically, it was expensive basketball sneakers. It wasn't until the mid to late '80s where there was some sense of crossover, when Anthrax performed in Public Enemy shirts and Run-DMC broke in on Aerosmith in "Walk This Way." It's funny seeing ripped jeans and leather jackets become so accepted amongst rap fans and rappers, even if the jeans are Balmain. And those Wes Lang Yeezus shirts wouldn't have been out of place at any metal show of the past 30 years.

A quick and dirty history of metal would begin in the late '60s in Birmingham, England, where Black Sabbath was founded. Some credit should also be given to Led Zeppelin, founded around the same time, in London. The sound then spread to the West Coast of America in the late '70s via 'The New Wave of British Heavy Metal,' led by acts like Iron Maiden, Judas Priest, and Diamondhead. The music was characterized by high-pitched vocals, screaming guitar (often with dual leads), and furious drumming.

Once in California, metal splintered into glam (think Mötley Crüe, basic riffage and semi-elaborate costumes) and thrash (think Metallica and Slayer, denim and leather and guitar-based music played as loud and fast as possible). The evolution continued after the pivotal year of 1986, which served up Slayer's Reign in Blood and Metallica's Master of Puppets—Pantera's skull-crushing Vulgar Display of Power released in 1992—but that was more or less the pinnacle. The less said about so-called "nu-metal," the better.

[A brief note on "black metal." This is not metal made by black people, rather a Norwegian offshoot of heavy metal who actually took the over-the-top "Satanic" imagery of early '80s bands like Venom seriously. So while bands like Mayhem and Emperor may not be as heavy as American acts like Slayer or early Metallica, they and their ilk have actually burned down churches and murdered people (including, but not limited to, each other). The book Lords of Chaos is essential reading on this phenomenon.]

Motörhead, perhaps the best of the proto-metal bands (and still going nearly 40 years after their founding), coined the term "Everything Louder Than Everything Else," which would serve as a fitting epitaph for metal. But, like rap, metal will never die. Here's your primer.