Dehumanizer (1990–1993)

While on his own Lock Up The Wolves US tour in August 1990, former Black Sabbath vocalist Ronnie James Dio was joined on stage at the Minneapolis Forum by former Black Sabbath bassist Geezer Butler to perform "Neon Knights". Following the show, the two expressed interest in rejoining Black Sabbath. Butler convinced Iommi, who in turn broke up the current lineup, dismissing vocalist Tony Martin and bassist Neil Murray. "I do regret that in a lot of ways", Iommi said. "We were at a good point then. We decided to reunite with Dio and I don't even know why, really. There's the financial aspect, but that wasn't it. I seemed to think maybe we could recapture something we had".

Ronnie James Dio and Geezer Butler joined Tony Iommi and Cozy Powell in the fall of 1990 to begin working on the next Black Sabbath release. While rehearsing in November, Powell suffered a broken hip when his horse died, falling on the drummer's legs. Unable to complete work on the album, Powell was replaced by former drummer Vinny Appice, reuniting the Mob Rules era lineup, and the band entered the studio with producer Reinhold Mack. The year-long recording process was plagued with problems, primarily stemming from writing tension between Iommi and Dio, and some songs were re-written multiple times. "Dehumanizer took a long time, it was just hard work", Iommi said. "We took too long on it, that album cost us a million dollars, which is bloody ridiculous". Dio later recalled the album as difficult, but worth the effort. "It was something we had to really wring out of ourselves, but I think that's why it works", he said. "Sometimes you need that kind of tension, or else you end up making the Christmas album".

The resulting album, Dehumanizer was released on 22 June 1992. In the US, the album was released on 30 June 1992 by Reprise Records, as Ronnie James Dio and his namesake band were still under contract with the label at the time. While the album received mixed reviews, it was the band's biggest commercial success in a decade. Anchored by the top 40 rock radio single "TV Crimes", the album peaked at number 44 on the Billboard 200. The album also featured the song "Time Machine", a version of which had been recorded for the 1992 film Wayne's World. Additionally, the perception by many fans of a return of some semblance of the "real" Black Sabbath provided the band with some much needed momentum.

Black Sabbath began touring in support of Dehumanizer in July 1992 with Testament, Danzig, Prong, and Exodus. While on tour, former vocalist Ozzy Osbourne announced his first retirement, and invited Black Sabbath to open for his solo band at the final two shows of his No More Tours tour in Costa Mesa, California. The band agreed, aside from vocalist Ronnie James Dio, who said: I was told in the middle of the tour that we would be opening for Ozzy in Los Angeles. And I said, "No. Sorry, I have more pride than that." A lot of bad things were being said from camp to camp, and it created this horrible schism. So by the band agreeing to play the shows in L.A. with Ozzy, that, to me, spelled out reunion. And that obviously meant the doom of that particular project.

Dio quit Black Sabbath following a show in Oakland, California on 13 November 1992, one night before the band were set to appear at Osbourne's retirement show. Judas Priest vocalist Rob Halford stepped in at the last minute, performing two nights with the band. Iommi and Butler also joined Osbourne and former drummer Bill Ward on stage for the first time since 1985's Live Aid concert, performing a brief set of Black Sabbath songs.