English poet and essayist Thomas De Quincey speculated, in his own Confessions of an English Opium-Eater, that the mysterious figure was Coleridge's doctor, P. Aaron Potter, who regularly supplied the poet with laudanum.
If the Porlock interruption was a fiction, it would parallel the famous "letter from a friend" that interrupts Chapter XIII of Coleridge's Biographia Literaria just as he was beginning a hundred-page exposition of the nature of the imagination.