The Italian Version

Heavy metal is a musical genre born in the 70s, mainly from the works of bands such as Led Zeppelin, AC/DC (but these bands weren't so heavy), and properly Motorhead, Blue Oyster Cult and Black Sabbath - although each one of these bands had a different approach.

The distinctive traits of heavy metal are the use of distorted electric guitar, in an evolution of the style pioneered by Jimi Hendrix; fast, hard drumwork with abundant use of double pedal (Motorhead and Judas Priest were real fanatics of this device) and often raw vocals. This is very generalistic, tho, because sub-genres can be very slow (like doom, which had a brief life in Britain in the early 90s) but still heavy, while Manowar are often fast but do not rank very high on a heavyness scale.

Then the genre prospered and evolved, and in the late 80s, propelled by the huge success of Metallica, Megadeth and Iron Maiden almost became mainstream - almost, because Metal always lacked that something to make it widely accepted. Maybe because metalheads have a scarcely palatable image, with truculent black T-shirts, boots and leather jackets. Or because its very sound is too heavy for most ears.
Iron Maiden are a particular case, anyway: they had a huge, huge success in Italy, so much that the Maidens themselves adopted some looks of the Italian metalheads. And also, Iron Maiden are about the band with the most references to pop(ular) culture you can find - Where Eagles Dare, The Prisoner. But not just that: another song is a renewed version of the poem The Rhyme Of The Ancient Mariner, and you can even find an Alexander The Great in their discography. No, they're not satanists either: the famous song The Number Of The Beast is inspired by a nightmare.

In the mid 80s, anyway, more extreme forms of Metal emerged: thrash, following (and evolving) Metallica, and Death Metal which rose from the swamps of Florida.
An archetypal thrash band are Slayer: extreme speed and very heavy riffs, plus vocals more similar to screams of anger and fury than anything. And lyrics which deal with themes most normal folks prefer to leave untouched - see Angel Of Death for example.
Thrash was born in the USA, but soon good bands emerged all over the world: Sepultura from Brazil (shame Sepultura were quite on the lefty-moonbat side regarding politics, because their music truly kicked ass) and the German triad Sodom-Kreator-Tankard that ravaged Europe with raw thrash (and uncounted liters of beer). Sodom are a band quite obsessed with military themes, and curiously enough they had a noticeable success in the war-torn ex-Jugoslavia (I remeber seeing on TV the logo Sodom sprayed on a bullet-ridden wall somewhere in that country)

But Death Metal brought things to an even higher (or lower, if your prefer) level: the first band of this kind were probably Death (what a coincidence) with their album Leprosy: to the fast and heavy riffs they added a growling voice describing in detail the effects of leprosy (and featuring the drawing of a leper on the cover).

For some reason, a lot of Death Metal bands come out of Florida: Obituary, one of the heaviest of the lot; Morbid Angel, Deicide, Malevolent Creation, Cannibal Corpse and more - if you suspect that some of these have a fascination for Satan & co. you're right.
The staple of Death is growling voice - that goes from an angry, raw voice to an unintelligible low-keyed continuous growl; the masters of which are Obituary and Cannibal Corpse (plus the spin-off bands Nile and Six Feet Under). The lyrics of these bands can be crazy, sick or even fun - in a certain way.
While these Floridians basically had a good time, the British Carcass were equally brutal, but grimmer... or maybe was it just British humor? Come on, "ultimate excretion of rabid globular neoplasm" cannot be serious.

The first two Carcass albums, and the works of their mates Napalm Death (who are much more committed in a political sense), gave birth to the extreme genre known as Grindcore: fast and brutal, growling and short songs about death, decay, rotting and such. A truly genial Grindcore band are Anal Cunt: they just growl, saying nothing or short silly sentences like "Shut Up Mike". 40 - 60 songs per CD, and alot of fun just reading the titles.
Also porno-grind does exist, and as you may have imagined their short lyrics are XXX-rated, same as the covers of their CDs (no, I'm not an expert of this stuff).

The people of northern Europe, probably affected by a lack of sunlight, gave birth to another genre, known as Black Metal. The roots of it probably can be found in Venom - a band from Newcastle, about as rough as working class northern englishmen can be and explicitely satanist (and absolutely lacking any musical skill). These crazed Norwegians took things one step further, with obscure, obsessive music (also fast and technical, often), sick lyrics, haunted voices and pagan cults. They also took a lot of names from The Lord Of The Rings - of the bad guys, of course. When I say sick, I mean it: Mayhem's singer killed himself, and the other guys in the band found the picture of his blown brains fit for a CD cover. Burzum (aka Count Grishnack) was so much into his stuff that he torched a couple of churches and finally killed another black metaller and ended up in jail. And other folks of the gang had similar stories. The black metal phenomenon is marginal nowadays, and most of the bands are nice guys who wear pentagrams and truculent face-painting only when on stage.

Also death metal found a sizable following in Sweden, and it was re-adapted to a more melodic and technical from by Dark Tranquillity, At The Gates, In Flames. At The Gates are one of my favourite bands, but sadly they were deep into post-modernist and existentialist stuff, sigh. But the pedalwork on Blinded By Fear is still awesome.

This is just a rapid exposition of the whole Metal scene - I left off the new (and silly) sensations of new metal and crossover, the likes of Linkin' Park, Limp Bizkit and Korn.
But I don't like that stuff anyway. There are also bands with a special status, like Motorhead, AC/DC, Kiss: they became so legendary to be something apart. But I'm never been a fan of Kiss - I only like God Of Thunder. However, Kiss were the first ones to use face painting (probably). There are fringe bands, like the Italian Death SS (where SS stands for Steve Silvestri, the founder) that became (in)famous for having skimpy but fat lesbian dancers performing a chicken sacrifice on stage... yes, Metal gigs can be really weird at times.

Let's see, Pantera's singer Phil Anselmo sometimes walked on stage so drunk (if not on high) he could barely speak, and at one concert they projected marijuana leaves around the hall with spotlights (not that the crowd needed any encouragement to use said herb). Cradle Of Filth had a performer grinding her steel thong with an angle grinder on stage.
A band called Zyklon B (feel free to feel outraged) is deeply into leather feticism and recorded the worst and most hideous album I've ver had the displeasure of listening.
Manowar... well, what can you say of people who ride Harley Davidson and pose wielding swords and wearing cowskin panties, and sing things such as "Other bands play, Manowar kill" or "Wheels Of Fire Burn The Night Ride Across The Sky"? Just try to listen to them once: you may either be raptured or repelled, eh...

But, from a sociological standpoint, Metal is the music of Western White Men - and in fact, some bands are strongly in the right wing (even too right, occasionally). Metal was born in Britain and the USA, and all the founders were basically white - and not shy of their whiteness. Megadeth's singer Dave Mustaine sports a T-shirts with barred hammer&sickle on the back cover of their So Far So Good... So What! album and one of their songs says: "What do you mean, "I couldn't be president, of the United States of America"? Tell me something, it's still "We the people", right? [Chorus: (repeat)]If there's a new wayI'll be the first in line,But, it better work this time.". Kinda constitutionalist, I'd say.

Of course there are metal fans and musicians of any colour, but not so many. I've seen a Sikh guy with his turban and a metal t-shirt, tho. Other places where Metal has a sizable following are south America and Japan - which is the most open to western influences of Asian countries. Quite a few metal bands also are openly and definitely on the left, so one cannot honestly say that Metal is monolithic a fascist. Still, Metal remains a realm where political correctness gained almost no footing, and it's much better this way.