Black Sabbath were a band made up of working-class kids from Birmingham. Their guitarist lost the tips of two fingers while working in a sheet metal factory. After that, he tuned his guitar down three semitones to make it easier to play. This led to the Sab's trademark deep, dark, nasty sound, which became the basis for a million impersonators and emulators (and also to Ozzy's awful reality show, but never mind that).
You can't understand metal unless you realise that it came from white working-class kids in England who worked in factories and wrote songs with titles like "Paranoid" even though they didn't actually know what the word meant. Similarly, you can't understand reggae unless you know what Jamaica was like in the 1970's and why. But that's another story which I'm not qualified to tell.
Sadly, you also have to understand how the record business works to understand why the longer a band goes, the more it is led to compromise what made it great in the first place in the service of producing saleable product. Black Sabbath are sadly neither the worst nor the best of bands in this regard - one of these days I will post about Yes, one of my favourite bands for a long time, and show how their addiction to record company largesse led them into all sorts of unpleasantness.