end of the 60's: Judas Priest, Scorpions, Black Sabbath, Deep Purple, Led Zeppelin, Uriah Heep and loads of other heavy acts form.
1973 AC/DC form to give the oldies a kick in the butt! But also other classic acts like UFO, Rainbow, Accept or Ted Nugent form.
end of the 70's: NWoBHM, bands like Iron Maiden, Tygers of Pan Tang, Tyson Dog, Atomkraft, Witchfinder General, Diamond Head, Blitkrieg form and make shit heavier than ever before. Bands like Raven, Venom and Avenger even introduce the world with genuie speed/thrash metal.
At the same time the punk movement soars to great hieghts. The more "hardcore" acts like Discharge, The Exploited, GBH or Broken Bones inspire the young metal bands to mix their NWoBHM with a lethal dose of agression and attitude.
So in the early 80's the thrash movement starts off with bands lik Slayer, Exodus, Sodom, Anthrax, Destruction and Kreator.
Also in the early 80's we see the first band that come from a punk background and start to incorprorate metal elements in their music. Crossover is born, bands like SOD, DRI, Suicidal Tendencies, CroMags, Agnostic Front or Excel.
In the late 80's we get the "second wave" with more technical and melodic thrash metal. Bands like Despair, Artillery, Testament, Forbidden, Vio-Lence, Defiance, Panic, Realm or Toxik.
In the early 90's grunge is the next big thing (the good side was it also killed Hair Metal!). The metal bands that were left mostly changed their sound and only a few metal bands were innovative enough to reach the masses. I remember PanterA and Sepultura broke through big time. Tough probably more in the US than here in Europe. I quite soon lost interest in anything after this.