Dr John is the recording name of new orleans r'n'b pianist Mac Rebinac. He is great. I started listening to him in the early seventies when he was known as dr john the night tripper.
another famous pianist from new orleans (now deceased) is doctor professor longhair.
in new orleans at a certain time musicians added titles of education to each others names as a sign of respect. Much like basketball player julius irving was known as dr J.
pi