FretBuzz
Monkey Man
For me the sonics of Heavy Metal developed from 1966 to 1969, starting with Cream, Jimi Hendrix Experience, Blue Cheer, Mountain, and Led Zeppelin. There were probably a lot of others in that time period I've never heard of but you might include the early proto-punks too (The Stooges, MC5, etc.). Then Black Sabbath came along (and Alice Cooper too, I guess) and stuck a dagger in the heart of the hippy era of proto-metal. Whenever I see some of those VH1 list type programs Black Sabbath gets a lot of mention as the first "true" metal band. I don't have a problem with that. So what's the answer? For me it started with Cream and Hendrix. I get the same head banging, horn throwing, air guitar playing vibe from those two (especially Cream) that I get from Metallica or Iron maiden.
Excellent points. Before The Jimi Hendrix Experience came along, the biggest 'guitar freak-out' album in rock was the Yardbirds' Roger the Engineer record, featuring the playing of Jeff Beck.
Another important "missing link" in the Yardbirds-to-Led Zeppelin evolution was the first album by the Jeff Beck Group. Jimmy Page used that as a blueprint for the hard-rockin' bluesy sound of Led Zeppelin I (Zep even played one of the same songs that Beck had done,"You Shook Me").
Cream was also definitely a link between the Yardbirds' bluesy rave-ups and heavy metal. (and don't forget that Clapton was the first rock guitarist to use Marshall amps, on his album with the BluesBreakers...Marshall amps definitely were a part of the evolution of metal).
IMO, the heavy metal sound didn't fully crystallize until the first Black Sabbath album (even though Iommi used Orange amps... they're very similar to Marshalls' sound). Partially it was Iommi's using so many minor chords, along with his throwing 'the devil's interval' tritone in here and there. It was also Ozzy's singing...he sounded like a doomed madman, with the demons closing in on him at any minute, with lyrics that were rich with dark, occult imagery.