Even after all these years Ozzy Osbourne is still a little baffled about how Black Sabbath came to be such a respected band.
"It's a really weird thing," says the singer, who turns 64 next week, "because what we did, we just did. We didn't go, 'Oh, we're going to write this way, and we're going to record that way, and it's going to come out like this'. And 45 years up the road who would have thought it's still going to be current and people were going to look upon it as the foundations of heavy metal?
"I mean, you don't realise that sort of thing, you just do it."
The Prince of Darkness is right though: with their thudding, heavy blues-soaked psychedelic rock songs like War Pigs, Paranoid, Iron Man, and Supernaut, and the run of five classic albums, starting with their self-titled debut in 1970 through to 1973's Sabbath Bloody Sabbath, Black Sabbath were the original heavy metallers.
This early Sabbath period influenced everyone from Iron Maiden, Metallica and Slayer to Guns N' Roses, the Foo Fighters and Queens of the Stone Age, as well as impacting on all sorts of metal genres from thrash and death to industrial and glam.
But then Osbourne, who's in a chatty mood on the phone from Los Angeles ahead of Sabbath's return to New Zealand next April for the first time in 40 years, is also still trying to get his head around that term "heavy metal". He can't stand it. "Because not everything Black Sabbath did was about the devil, or about heavy metal because Changes was a beautiful song. But all they ever remember is that I sing about the devil and Iron Man, you know."
Not that Osbourne laughs out loud much these days, but he is joking, kind of. Because Black Sabbath were always more than just a heavy metal band, with songs like the trippy and dreamy Planet Caravan, the song Sabbath Bloody Sabbath, one of the group's best, was a mix of bludgeoning and breezy, and that song Osbourne mentioned, Changes, is a stunning serenade off 1972's Black Sabbath Vol. 4.
The last time Black Sabbath toured here, headlining 1973's Great Ngaruawahia Music Festival, they played Changes, a song they have only ever played twice in concert.
But also, just before their set, they asked for a cross to be burned on stage at midnight, which, you have to agree, is pretty heavy metal.
"Oh, I can't remember, that was a long time ago now," says Osbourne of the visit, though he does remember the official Maori welcome.
The original Black Sabbath, made up of Osbourne, guitarist Tony Iommi, bass player Geezer Butler and drummer Bill Ward have re-formed a number of times over the years. And though Ward is not part of this reunion, it is significant because they are also recording their first album in 33 years, the first since Osbourne was asked to leave the band because of his outrageous drug use.
They haven't seen eye to eye on a number of things over the years, squabbling about rights to the band's name and other contractual issues, but apart from Ward, all is well in the Sabbath camp these days.
"What's different now is that none of us get drunk or stoned or any of that stuff," says Osbourne. "We're all clean, and all in control of ourselves, we're not intimidated by each other, there are no arguments, and it's the way it should be.
"But when we were kids we had egos. When you're 21 and you get some success it takes a while to get your head around.
"You have an ego, you have the spoils of success, the cars, the houses, the money, the alcohol, the drugs, the groupies, and all the rest of it, and if you go through all of that and you are lucky enough to survive you get married, you get divorced, you get married again, and it's a journey.
"But we've done it all so what it boils down to now is the music - and that's what got us where we are in the first place. We have come through the other side, we're still able to work together, and that's where the enjoyment comes from. It's been a lot of fun making this record."
The recording has been interrupted by Iommi's diagnosis with lymphona at the beginning of this year. But Osbourne says the guitarist is back on track after treatment, "which has been a bit rough on him but he still manages to come up with those great riffs".
"It's been more than 30 years since I really seriously worked with the guys. We had a try a few years back but nothing came of it. But for some reason the timing is right and we've done about 15 songs.
"Black Sabbath is very unique in the respect that nothing is formulated. It's very unpredictable. I just hope the people who have waited all these years aren't disappointed."
Who: Black Sabbath
Where and when: Vector Arena, April 20
Tickets: On sale at 9am tomorrow from Ticketmaster.
More info: livenation.co.nz
Essential listening: Black Sabbath (1970); Paranoid (1970); Master of Reality (1971); Black Sabbath Vol. 4 (1972); Sabbath Bloody Sabbath (1973); Sabotage (1975)