Black Sabbath

Black Sabbath is arguably one of the greatest metal bands of all time, all while arguably not even being a metal band. Funny how things work out that way.
When people think of Black Sabbath (and hopefully know who they are) Ozzy Osbourne would probably come to mind, which is fair. He did have a lot to do with the band in general, and he gave the band it's first name, The Polka Tulk Blues Band. Apparently he came up with it when he found a cheap brand of talcum powder he saw in his mother's bathroom. They then shortened the name to just Polka Tulk, and then eventually changed the name to Earth. Fun Fact: Ozzy HATED that name.
They stuck with that name for a while, thinking they were going to be more of a blues rock band until they saw a movie called Black Sabbath. They wrote a song with the same name, obviously inspired by the movie which is arguably the heaviest song ever written based entirely on the pure evil vibe it gives off. After that, they changed their name to Black Sabbath and started writing more songs of the same nature. Evil, heavy, and freaking awesome.
The Ozzy years are characterized as "heavier, and more political." Heavier, sure? Political, very yes. War and politics were topics that were always used during the Ozzy years. With songs like, War Pigs, they often criticized the governments of the world as, well, war mongering pigs. I'm not one for politics, but these songs are freaking amazing. The lyrics are meaningful, while at the same time feeling like a total diss to whoever Sabbath wanted to go against. The music itself, as in instrumentation and melodies, brilliant. In the world of hard rock/metal, I would almost say that Black Sabbath was The Beatles of that genre. They truly dominated; nothing could touch them.
Ozzy got kicked out in 79, and was later replaced with Ronnie James Dio, who was the vocalist for Rainbow (AKA: Elf plus Ritchie Blackmore). I've talked about Dio before, but let me say once again that he was perhaps the greatest metal vocalist of all time. As for how Black Sabbath changed because of Dio, well, for one, Dio had a completely different voice, different attitude, and different style of writing with a different approach altogether. Dio didn't often follow the riff of a song for his melodies whereas Ozzy did it more than not. Which era was better, though? In my opinion... I have no idea. I don't really think it's fair to compare because they're so musically different.
After Dio left, Sabbath got Deep Purple vocalist Ian Gillan to replace him, and then he left after a couple albums to form a band called Blue Murder, so they replaced him with Tony Martin. I'm not going into them, because I don't really care for those years as much. That's kind of when I stopped listening to them. Up until they got Ozzy back, and they made their new album, 13, which is freaking awesome. Go buy it.
Holy hell, this is long. Sorry for also making it a history lesson, I just love Black Sabbath. <3