Dismayed by Deep Purple’s move towards funk and soul-influenced material, guitarist Ritchie Blackmore formed Rainbow in 1975 to pursue his vision of unsullied hard rock. Rather than assemble a new band, Blackmore simply hijacked Elf, who had opened for Deep Purple in 1974. Blackmore formed an immediately bond with Elf’s lead singer, Ronnie James Dio, and from that partnership came early Rainbow classics like “Man On the Silver Mountain,” “Self Portrait” and “Snake Charmer.” The formula was surprisingly prescient. Ritchie Blackmore’s Rainbow lays the early blueprint for bands like Iron Maiden and Judas Priest, who would lead hard rock into its next phase. The album’s other great contribution is its medieval-themed epics. With imagery of knights and castles and eternal glory, “The Temple of the King” and “Sixteenth Century Greensleeves” heralded the epic fantasies of heavy metal’s future. Dio was Rainbow’s breakout star, but the album belongs to Blackmore, and in the finale — the instrumental “Still I’m Sad”— he wields his guitar like a mighty swordsman.