Black Sabbath
Original "Heavy Metal" band, they started it all, and are such an amazing group.
Iron Maiden
Pioneers of Heavy Metal and NWOBHM - astounding group to this very day.
Judas Priest
Along with Iron Maiden, pioneers of heavy metal and NWOBHM, astounding group, not a big fan of their recent releases.
Ozzy Osbourne
Original vocalist for Black Sabbath, absolutely stellar solo career. Not a fan whatsoever of his more recent stuff.
Dio/Rainbow
Dio. God of Metal. His solo career, along with his work in Rainbow are among the best metal acts of the '70s-'90s.
Recommendations..
Black Sabbath - Black Sabbath, Vol. 4, Sabotage, Heaven and Hell
Iron Maiden - Killers, The Number of the Beast, Seventh Son of A Seventh Son, Powerslave
Judas Priest - Stained Class, British Steel, Unleashed in the East, Sad Wings of Destiny
Ozzy Osbourne - Ozzmosis, No More Tears, Ultimate Sin, The Essential
Dio - Holy Diver, The Last in Line, Strange Highways, Dream Evil
Rainbow - Ritchie Blackmore's Rainbow, Rising, Long Live Rock 'n Roll, On Stage