I think the Kinks made the first metal chords I recall....What year was Donovan’s Hurdy Gurdy Man?.....that has metal chords for sure
Led Zeppelin was more hard rock than metal though some songs like WLOL or WTLB have it in them
Sabbath likely the first true metal band....planet caravan was an exception to their metal roster of songs....a beautiful piece btw to me
“In The Garden of Eden” ...another early metal sound...I’m sure anyone on this thread understands
Purple Haze....metal ish
Touch by Deep Purple ....same
Some early Zappa licks ....
Amboy Dukes...early 1968
It’s impossible to say but Black Sabbath truly ran with it
Robin Trower could have but his Procol Harem stuff which was early was not
The Yardbirds especially with Page and Beck together briefly coined some licks tha were metal and that was fairly early
King Crimson’s 21st Century Schizoid Man, from 1969, is pretty metal sounding.
Blue Cheer, circa 1966. Would they be the first?