I've long been a John Martyn fan and have several of his albums. His guitar playing broke new ground.

https://www.guitarworld.com/artists/guitarists/why-john-martyn-was-an-underrated-guitar-genius

Much in the same way that his tunings were selected for fullness and warmth, to make up for the lack of other instrumentation, Martyn’s slap-and-pop technique adds rhythm and bite. In a sense, his right thumb was his drummer.'