OUT NOW: Black Sabbath, HEAVEN AND HELL and MOB RULES Deluxe Editions

It was one of the most vital eras in Black Sabbath history, and the band's legendary original vocalist, Ozzy Osbourne, wasn't even a part of it. While Ozzy was charging headfirst into his iconic solo career with the brilliant Randy Rhoads on guitar, Sabbath had recruited former Rainbow singer, Ronnie James Dio, to take his place.

"I'd heard Ronnie when Ritchie [Blackmore] put out the first Rainbow album [after he left Deep Purple]. Obviously, you'd say, 'I wonder what Ritchie's band's like,'" Tony Iommi told Rolling Stone. "I liked the album, and of course, I loved Ronnie's voice, not thinking for a minute we'd ever end up together. He's always had a real strong, powerful voice."

The combination of the two heavy metal entities resulted in a pair of instantly classic albums: Heaven and Hell (1980), and Mob Rules (1981), both of which arrive today in deluxe editions packed with extras.

"I think definitely it probably wouldn't have worked with anybody apart from Ronnie because of how enthusiastic he was and how he got into the music straight away," bassist Geezer Butler raved to Rolling Stone. "And his voice is incredible anyway."

While the union only lasted long enough for two studio albums and one live effort, Live Evil, Black Sabbath's Dio era is one that remains near and dear to the hearts of the group. According to Butler, his relationship with the late singer was something very special, albeit incredibly volatile.

"We used to argue like husband and wife. We would really go at it. And it's hard to find people like that that you can really, really slag, and then the next day go and have a drink with them," Butler reminisced. "It's like being back in my family again, like the Irish family. Ronnie was totally outspoken. You always knew where you were with him, that's for sure. And that we used to argue and stuff' and then make up and be best friends. And we were best friends when he passed away. I still go to his grave every year."

"I really was proud of those first two albums, certainly when we'd done Heaven and Hell," Iommi added. "It was a new thing for us -- and a daring thing, in some ways -- to change your singer. It's easy to fall by the wayside, and we didn't, because we believed in what we were doing. So those albums mean a lot to me."