Answer
Ronnie James Dio replaced Ozzy Osbourne as lead singer of Black Sabbath in 1979. Dio had previously fronted the bands Rainbow and Elf. He brought a more theatrical element to Black Sabbath's music, and the band released several successful albums with him as lead singer, including Heaven and Hell and Mob Rules. Dio left Black Sabbath in 1982, and was replaced by Ian Gillan.