What was the most important innovation in popular music in the last century? I would say it was the use of the electric guitar as a lead instrument (ie., not just an accompaniment to singing). Great blues artists like Albert, BB and Freddie King started it, and then it exploded into the mainstream in the late ‘60s and early ‘70s, with the Yardbirds, Cream, Hendrix, Deep Purple, and Led Zeppelin, among others.