Don't get me wrong -- in the narrative as I reconstruct it, Black Sabbath certainly gets given their rightful pride of place. They possess a napoleonic status of "first among equals." I'd even go so far as to say that without Sabbath, metal might have coalesced rather differently -- and perhaps less powerfully, less coherently -- as a genre. But it's a mistake to portray them as the sole seminal band.
Halford's claims -- which I was surprised to hear him making on stage during their Epitaph tour -- get magnified in Garry Sharpe-Young's rather lopsided and misleadingly-named compendium Metal: The Definitive Guide (for my critical review of that work, see here), which unfortunately gets taken as a major source for the Wikipedia Traditional Heavy Metal entry. Interestingly, some go Halford one better, for instance Roy Wilkinson, in this 2010 Guardian piece, claiming that Judas Priest invented heavy metal!
Earlier on, it was common to point towards a triumvirate of late 60s-early 70s heavy metal originators -- Sabbath, to be sure, but also Led Zeppelin and Deep Purple -- and to tilt the hat towards a few other heavy bands as predecessors, for instance, Blue Cheer, Cream, Jimi Hendrix, Vanilla Fudge, and even Steppenwolf (since they have that "heavy metal thunder" line in Born to Be Wild). There's certainly more truth there in that expanded genealogy, I think, but it doesn't go quite far enough.
I tend to think that Heavy Metal as a musical genre, in its classic 70s-early 80s forms, has a history analogous to Existentialism as a philosophical movement. The time-frame is much shorter for the former, to be sure, since it took close to eight decades for the earlier figures who would prove so central as influences on the later movement (Kierkegaard, Dostoyevsky, Nietzsche, Shestov, Rilke, Kafka to be brought together under that rubric, and recognized retrospectively as having inaugurated a new kind of philosophy. In the case of Heavy Metal, we're really looking at a space of a decade, whose limits let's set, admittedly arbitrarily, from 1967 to 1977.
And again, let's emphasize the absolutely central role of Black Sabbath in the development of metal -- that string of early albums, Black Sabbath (1970), Paranoid (1970), Masters of Reality (1971), IV (1972), Sabbath Bloody Sabbath (1973), and Sabotage (1975). There's a massively influential body of work there -- and keep in mind that by that time Toni Iommi is already working with a protege band, Quartz, who are touring with Sabbath and AC/DC in 1976.
But who else deserves their place in the limelight, or at least a mention (and, like I said earlier, some follow-up posts) as key players in the emergence of heavy metal? Led Zeppelin is already on the scene, coming out out their first album in 1969 -- but although their influence is well-attested, I'm not going to say much about them. I'm much more interested in several of the other bands that are present at the origins.
Deep Purple, to be sure, gets started in 1967 -- but can we call Shades of Deep Purple or even The Book of Taliesyn metal? Not in any full sense -- although in their live shows by this time, they're certainly pushing into that uncharted territory. By the Mark II lineup, adding Ian Gillan and Roger Glover, at least on a number of songs, Purple is identifiably early metal -- Machine Head is already there as a reference point for new metallions in 1971.
Uriah Heep, who started out in 1969 and put out their first album in 1970, certainly deserves a place in the early history of metal as well. Structured similarly to Deep Purple -- vocal, guitar, bass, drums, and organs -- but with a clearly distinctive sound of their own, they likewise contribute some songs in the early 70s that not only are identifiable as metal, but which will become standards, and even get covered by later metal bands (e.g. Easy Living, by WASP).
Who else deserves a place in the pantheon of metal originators? In my book -- and I'm confining myself to bands that we can make a case for as being "metal", not just predecessors (like Blue Cheer) -- we'd have to include
- U.F.O. (already making metal with songs like Boogie in 1970)
- The Scorpions (Lonesome Crow appearing in 1972 -- when they lose Michael Schenkner to UFO on tour)
- Budgie (debuting in 1971)
- Blue Oyster Cult (Cities on Fire with Rock and Roll in 1972)
- Pentagram (doing what are clearly metal singles in the early 70s)
- Buffalo (an early 70s Australian, identifiably metal band)
- KISS (their debut album in 1974)
- AC/DC (their debut album appearing in 1975)
I'd even go so far as to include, but more on the penumbra, rather than right in the center, right at the start of the 70s (and yes, I know some of these groups start in the late 60s).
- Thin Lizzy
- Alice Cooper