Charlie Watts. By 1968-69, he was sporting pretty long hair. By 1976, he had gone in the complete opposite direction, toward a severe-looking buzz cut. Starting in the 80s, he went back to a length somewhere in between the two extremes, where he’s kept it most of the time since.
Roger McGuinn, Chris Hillman, Gram Parsons and Kevin Kelley of The Byrds cut their hair to play country music in 1968. McGuinn's hair was to his shoulders by 1970, longer than it had been previously.
