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 drummer Vinny Appice. The name Dio was chosen because it made sense from a commercial standpoint, as the name was already well known at that time.

Black Sabbath were an English rock band formed in Birmingham in 1968 by guitarist Tony Iommi, drummer Bill Ward, bassist Geezer Butler and vocalist Ozzy Osbourne. They are often cited as pioneers of heavy metal music. The band helped define the genre with their first three albums Black Sabbath, Paranoid and Master of Reality (1971). Following Osbourne's departure in 1979, the band underwent multiple line-up changes, with Iommi being the only constant member throughout their history.