Ronnie James Dio had some tough shoes to fill in 1980 when Black Sabbath asked him to be the singer to replace Ozzy Osbourne.

Both Sabbath and Ozzy had admittedly turned into sloppy, drunken, drug-using rock stars, but the difference was Tony Iommi, Geezer Butler, and Bill Ward had the upper hand on the insanity.

Ozzy, well, was a mess. And it was painfully obvious during Sabbath's 1978 Never Say Die! Tour when openers, a new band called Van Halen, ran circles around them every night.

Even before the tour, while recording the album, the lovable but erratic singer would disappear for days and weeks at a time. “Ozzy was going to clubs and getting really out of it and not coming home,” Iommi said in the oral history book, Louder Than Hell. “It got to a stage where nothing was happening with him. He came apart on us.”

Soon after the band fired Ozzy, Iommi was at a rock bar on the Sunset Strip in West Hollywood when he ran into Dio, who had just quit Rainbow. The two were in similar predicaments, which was a pleasant coincidence. Another coincidence, the bar they were at was The Rainbow. Trippy.

Sabbath without Ozzy was a scary situation for Iommi who may have invented the heavy metal genre but the younger bands like Iron Maiden, AC/DC and Mötorhead had taken that wicked '60s sound to a new level.

Dio had just left making music with the legendary Ritchie Blackmore who wanted to make more popular music instead of the dark, heavy rock Sabbath had perfected. The meeting was kismet.

Ozzy is rock royalty. No question.

But Ronald James Padavona's voice was from a land before time.

In the long and glorious history of rock music, his voice is easily identifiable, awe-inspiring, and a teensy bit evil.

When Ozzy sings "Iron Man," for example, it sounds like it should, a little scary, a little ominous.

When Ronnie James Dio sings it, though, it's delivered perfectly, intentionally, and with a sneer, not a hiccup.

So when Dio came in to record with Sabbath it was a win-win for all parties. Ronnie was back with not just a solid guitar player but one of the most legendary groups in hard rock. And Sabbath had a reliable singer who took their sound to the next level.

The results were a delight and a relief. Like AC/DC had done with Brian Johnson after Bon Scott had died, Sabbath had replaced Ozzy and the patient didn't just live, it thrived.

The only dent in the armor was Ozzy had joined forces with Randy Rhodes and a five months after Sabbath dropped the album Heaven and Hell, Ozzy released Blizzard of Oz packed with hits like "Crazy Train," "Mr. Crowley," and "I Don't Know."

Dio and Sabbath would record two more albums together and beautiful music was made. But Dio likes things his way. Iommi states that the first record Ronnie felt like a hired gun but by the second one, he wanted way more input.

He got it by going solo and making the 1983 classic Holy Diver which went double platinum.

And he followed it up with the equally powerful The Last in Line.

Dio saw diminishing returns with subsequent solo efforts and in 1992 rejoined Sabbath for a new album, Dehumanizer, which surprise surprise was good.

While touring it, Ozzy told the world he was retiring from rock. Two shows were scheduled at the Pacific Amphitheater in Costa Mesa, California. Ozzy asked Tony if Sabbath could open for him on those two shows, with all of them ending the night with a few songs together.

Sabbath open for Ozzy? Dio was not interested.

Especially not for Ozzy, a guy whose shadow he had fought to stay out of since he first accepted the job. Rock fans literally spit on the 5'4" Dio for having the gall to try to replace Ozzy in Sabbath.

So he quit the night before those shows and was replaced with Judas Priest singer, and friend, Rob Halford who only accepted the gig with Dio's blessing, which he received.

Thirteen years later, 2005, Sabbath cozied up with Ronnie James again to put together a greatest hits with a few new songs and call the whole thing, Black Sabbath – The Dio Years. The recording of the new tunes went beautifully and like old lovers reuniting, they agreed to tour. Which lead to a new album The Devil You Know.

But since Sabbath was still playing gigs with Ozzy, with original drummer Ward, and this new thing had Dio on vox and his longtime drummer Vinny Appice on drums they felt like a new name was needed, they chose Heaven & Hell after their 1980 sigh of relief.

Because Ronnie James Dio is magic, The Devil You Know was dynamite.

Skid Row singer Sebastian Bach agreed saying, "I think Ronnie James Dio's best ever song was his very last song, which was called 'Bible Black.'"

Bach continued, "how many artists can say that their last single was among their best. To me it's the best. You can put it on and thank me later."

The thing about this tour was it was only going to be Dio-era Sabbath and Heaven & Hell songs. Therefore the last three songs Dio ever sang live were "Heaven and Hell," "Country Girl," and "Neon Knights."

Those songs were professionally recorded in at the Wacken Open Air Festival in Germany a month before Dio's last show in New Jersey.

However, this footage of "The Mob Rules" the first song of his final show, that's just as special.

Dio, a big sports fan and specifically a New York Giants fan (ironic for the former singer of Elf) gets a shirt thrown at him about two and a half minutes into the song. He picks it up and investigates it and sees it's a Philadelphia Eagles shirt.

Dio throws it down on the stage, steps on it and delivers a finger gesture that is not his trademark devil horns - something legend has it that he made famous.

Neither Sabbath nor Ozzy have any tour dates scheduled.

But in a strange coincidence, Judas Priest's next show will be at Power Trip in Indio alongside AC/DC on Saturday night. Priest got the call after a legendary act cancelled.

Ozzy Osbourne.

Power Trip tickets are available here.