Probably the most controversial of all rock music for its lyrics and image. Its loud, aggressive music and characterized by the electric guitar play the central role in the music backed up with vocals, drumming and base. It branched off of psychedelic music and blues rock in the 60's. The original heavy metal band is no doubt Black Sabbath and it has been going on for 30-35 years.
The idealogy of the music is very romantic which means it is a praise of imagination, emotion and fantasy. Another central theme heavy metal obsessed apon is chaos which involves mental illness, confusion, war, hell demons and what not. Bands go at this theme to find excitement within it or deep personal and emotional involvement or it can be the band reflecting on the human condition from the outside. Finally, the prime reason of its controversy is its anti-Jeudo Christian imagery and themes like Satan, hell and evil. Like written earlier, metal bands make songs about evil because it goes back to chaos. Also, Jeudo-Chrisitanity is the very foundation of Western civilization and making negative (or anti) songs about it means it is the ultimate rebellion. She further explains why they make songs about evil to question society what is really profane. Yes, but there are still bands who use satanic imagery simply as a gimmick to look rebellious or simply just having fun being offensive. There are some themes of hedonism themes (sex, drugs, rock & roll etc) as praise or sometimes negative criticism. And some metal bands do start bands to blow off teen angst just like any other type of rock music. But the difference is, heavy metal is against the idea of rebellion to be cool and hip. So, understand there is more to heavy metal music than the old, tired "kill your mother/rape your dog" stereotypes.
It has branched out into many sub-genres over the years. It started in the early 70s with traditional metal and then New Wave of British Heavy Metal (NWBHM in short), then thrash metal and hair metal in the 80s. 2 children sub-genres Black metal and death metal arose in the late 80s from the parent thrash metal. The 90's is considered the depression of heavy metal when its popularity started to die down. Nu-metal/rapcore, which only a few of them should be considered heavy metal at all, became popular in the mainstream. Doom metal were born in the underground then in the shadow. Now in the 00's, metalcore bands are hitting mainstream while most nu-metal bands popularity withered away.
traditional metal - Black Sabbath and Judas Priest
New Wave Of British Heavy Metal - Iron Maiden and Judas Priest
thrash/speed metal - Slayer, Metallica, Anthrax, Sepultura, Overkill, Megadeth, and Kreator
hair metal - Motley Crew, Kiss, Poison, and Whitesnake
black metal - Burzum, Emperor, Mayhem, Enslaved and Dark Funeral
death metal - Death, The Possesed, Obituary, Morbid Angel, Bolt Thrower and Dying Fetus
nu-metal (most nu-metal shouldnt be even counted as heavy metal) - Korn, Deftones, Limp Bizkit, Slipknot, and Linkin Park
doom metal - Cathedral, Katatonia, Theatre of Tragedy and My Dying Bride
sludgecore - Crowbar, Eyehategod, Soilent Green and Iron Monkey
power metal - Manowar, Blind Guardian, Primal Fear and Memory Guardian
modern metal (or groove metal) - Pantera, Pissing Razors, Machine Head and Skinlab
metalcore - Lamb of God, Caliban, Killswitch Engage, and Annubus Rising