Dio was an American heavy metal band formed in 1982 and led by vocalist Ronnie James Dio. Dio left Black Sabbath with intentions to form a new band with fellow former Black Sabbath member, drummer Vinny Appice. The band released ten studio albums and had numerous lineup changes over the years, with Dio himself being the only constant member. Guitarists included Vivian Campbell, Craig Goldy, Doug Aldrich, Warren DeMartini, Tracy G, Jake E. Lee and Rowan Robertson.

The band dissolved in 2010 when Ronnie James Dio died of stomach cancer at the age of 67. Ronnie James Dio has sold over 50 million records worldwide.

In 1982, disagreements originating over the mixing of Black Sabbath's Live Evil album resulted in the departures of Ronnie James Dio and Vinny Appice from the band. Wanting to continue together as a band, the two formed Dio in October 1982 in Los Angeles with bassist, and Dio's former bandmate in Rainbow, Jimmy Bain and guitarist Jake E. Lee (formerly of then-up-and-upcoming bands Ratt and Rough Cutt). Not long after the band's formation, Dio parted ways with Lee (who would later join Ozzy Osbourne's solo band) due to musical differences, and he was replaced by Vivian Campbell. The following May, the band released their debut album, Holy Diver, which featured two hit singles – "Rainbow in the Dark" and "Holy Diver" – that gained popularity, in part from MTV. Dio and Bain played keyboards in the studio, but keyboardist Claude Schnell was recruited for live shows in 1983 prior to the Holy Diver tour. Schnell played to the side of the stage on the first two tours before coming out front in 1985. Dio had this to say of the band's origins:

It was a good time to be in that band. It was perfect for us. Everything just fell into place. The ethic in rehearsal was amazing. The effort in the recording was just as good. Everybody wanted it to be great. We really believed in what we were doing and couldn't wait to get that product out and have people hear it.

Now a quintet with Schnell on keyboards, the band released their second studio album, The Last in Line, on July 2, 1984. It was followed by their third album, Sacred Heart, which was released on August 13, 1985.

In 1985, Dio, Campbell and Bain also wrote the song "Stars" for the Hear 'n Aid project, with many other heavy metal luminaries of the time contributing. Campbell became unhappy working with Dio, and the rift between them culminated in Campbell being fired from Dio's band. Campbell was subsequently invited to join Whitesnake in 1987. Several songs were recorded live during the Sacred Heart tour for the 1986 Intermission EP with Campbell still on guitar, however the EP also contained the studio track "Time To Burn", which served to introduce fans to Craig Goldy as the new guitarist.

On July 21, 1987, their fourth album Dream Evil was released. After Dream Evil, Goldy, wanting to pursue solo projects, left the band. In June 1989, 18-year-old Rowan Robertson was announced as Goldy's successor but further changes were to follow, with Schnell, Bain and Appice leaving the band.

Schnell, Bain, and Appice were replaced, respectively, with Jens Johansson, Teddy Cook, and former AC/DC drummer Simon Wright. The new band released the album Lock Up the Wolves in the spring of 1990. During the tour, Dio had a chance meeting with former Black Sabbath bandmate Geezer Butler which led to that band's short-lived reunion, producing one album, Dehumanizer. After this, Dio reassembled Dio once again, bringing back Appice on the drums, but discarding everyone else. By early 1993, guitarist Tracy G, keyboardist Scott Warren of Warrant and bassist Jeff Pilson of Dokken had all joined. During this era, the band abandoned fantasy themed songs and focused on modern issues. As a result, some fans regard the albums made during this period—1993's Strange Highways, 1996's Angry Machines and the live album Inferno: Last in Live—as the worst in Dio's catalogue, while others view them positively as a step away from the outdated sound of the 1980s. With disappointing record sales for Angry Machines, management wanted the band to go back to their earlier style prompting the departure of Tracy G to be replaced by the returning Craig Goldy. In addition, Appice left Dio once again.