Which vocalist fronted Black Sabbath from 1979 to 1982?

Ronnie James Dio fronted Black Sabbath from 1979 to 1982, replacing Ozzy Osbourne as the band’s lead singer.

Dio joined after leaving Rainbow and quickly began writing with guitarist Tony Iommi. Their first Black Sabbath album together, ‘Heaven & Hell,’ was released in 1980 and introduced a more melodic but still powerful vocal character. The lineup followed it with ‘Mob Rules’ in 1981 and the live album ‘Live Evil’ in 1982.

Dio left Black Sabbath in November 1982 after tensions surrounding the mixing of ‘Live Evil.’ He later returned for the 1992 studio album ‘Dehumanizer,’ so his connection with the band was not limited to the original 1979–1982 period.

Ian Gillan, Glenn Hughes, and Tony Martin also sang for Black Sabbath at different times, which explains the possible confusion. They did not front the band during the period named in the question.