Watch Full Movie Online. This career spanning documentary on heavy metal legend Ronnie James Dio delves deep into his incredible rise from 50's doo-wop crooner, to his early classic rock days in Ritchie Blackmore's Rainbow, to replacing the iconic lead singer Ozzy Osborne in Black Sabbath, to finally cement his legend with DIO. Ronnie's biography is completely unique to the tired sex, drugs and rock and roll cliches. The film is about perseverance, dreams and the power to believe in yourself.