MGM·Lion
But there is no denying that every single radio DJ, on any channel, in the 60s-70s would keep introducing records with "And here's another from the King of Folk, Bob Dylan", & such locutions. That's when it all started. & still round & round goes the bloody great ☸

Nope. That's not when it started as illustrated by my link above which everybody ignored. Here it is again -
Progressive folk

Perhaps I should have put in a quote from it -
The original meaning of progressive folk came from its links to the progressive politics of the American folk revival of the 1930s, particularly through the work of musicologist Charles Seeger.[1] Key figures in the development of progressive folk in America were Pete Seeger and Woody Guthrie, who influenced figures such as Bob Dylan and Joan Baez in the 1960s. All mixed progressive political messages with traditional folk music tunes and themes.[2]