there were 3 bands that started in the late '60s who were called heavy metal but led zeppelin never accepted being a heavy metal band, deep purple was kind of a heavy metal band, but not fully, black sabbath was the only band of these 3 bands that was a heavy metal band.
apparently motorhead although they really sound like a heavy metal band is not a heavy metal band, lemmy said so. kiss is a heavy metal band. ac/dc is the only band where you can't prove they are heavy metal or hard rock.
lukejbarnett

Black Sabbath were the first, and some might say the best. Ozzy managed to be awesome even when he was out of his mind on drugs. - Maybe that helped!

I like a lot of his stuff however, I have a serious question.
What do you call his voice?
When I was a kid if you drank whole milk and started talking you would sound "Jewish" like Zoiberg the alien from Futurama.
It's a blee blee blee kind of voice.
Ozzy sings in that voice, so what is that tone called?
Baritone is deep for instance.
WEIRDLY…
The guy from Black Label Society has the same voice and he used to play with Ozzy!

He was the first true heavy metal artist. He founded the genre, or at least made it famous.
Plant a tree today.