Well first he was in a band called Elf.Later he was called by Deep Purple guitarist Ricchie Blackmoore to be on vocals to his solo band called Rainbow,he was in it from about 5 albus but then he left because it was going to be comerical rock and DIO didnt really like that,after he left he whent to replace Ozzy for Black Sabbath and sang with them for a few albums,then he was kicked out because Ozzy returned,DIO started his own band that got pritty succesful,then he was in and out from Black Sabbath for a few times,then he joined in the band called Heaven and Hell (name from an album on which DIO sang with Black Sabbath) the band was made of old Black Sabbath members.Dio planed to return to his solo group after his cancer got cured but well...DIO died,on the 16th May 2010,why are you asking?