I know I've written about this before, but have patience with me as I make a new point. There were two occasions in pop/rock music, pretty close together in '69-'70, where Everything Changed:
The first Led Zeppelin album came out in January 1969.
The first Black Sabbath album was released in February 1970.
Upon hearing both albums, every musician I knew realized that the bar had been raised, and music was entering new territory. And while the bands were really quite different, they do share many influences as well as mythologies: both are often mentioned as the first "Heavy Metal" band.
While both are indeed heavy, I think Sabbath is a better candidate for the title, as Zep, under Jimmy Page's direction, was a more experimental, blues-driven group, where Page could use Robert Plant's unique vocals as part of an orchestration along with guitar tones that were different and pretty exciting.
But Sabbath had the hands-down edge in Heavy, with Tony Iommi's use of what came to be known as power chords, and simplistic, insistent, and compelling "riffs", or repeated musical motifs.
So did Iommi invent the use of "power chords"? For those unfamiliar with the term, a power chord is a note grouping using just root and fifth notes, with no third. Thus, a C power chord would use C & G notes, with no E. This means that there is no 'major' or 'minor' distinction, but rather a universality of a solid chord. The 'prettiness' of the major, and the 'darkness' of the minor are non-existant, and all that remains are the solid, resonant foundation of the chord.
And back to the question, did Iommi invent power chords? No. Several players and bands were exploring these chord formations, including a certain Mr. Hendrix. But who actually used them first?
The first real usage of the power chord was much earlier, in my opinion, and it was by the unlikely but very talented Scotty Moore, guitarist for Elvis Presley, in the recording of Hound Dog. The song, originally recorded by Big Mama Thornton, is what is called a "12 bar blues" format. A chord chart would look like this:
with each Roman Numeral representing the chords of the progression relative to the root key. If the song is in the key of E, then I = E, IV = A, and V = B.
All this is to set up the following premise: Listen the the original recording of Hound Dog, and listen to what Scotty Moore is playing on the I chords: Root-fifth notes, with no thirds. And thus was the power chord born.
Oh, and listen to the solo. Pretty serious rock chops for the day. For both of those, Scotty Moore is the latest Under-Appreciated Guitarist in the series.