The Person from Porlock was an unwelcome visitor to Samuel Taylor Coleridge who called by during his composition of the oriental poem Kubla Khan. Coleridge claimed to have perceived the entire course of the poem in a dream (possibly an opium-induced haze), but was interrupted by this visitor from Porlock (a town in the South West of England, near Exmoor) while in the process of writing it. Kubla Khan, only 54 lines long, was never completed. Thus "Person from Porlock", "Man from Porlock", or just "Porlock" are literary allusions to unwanted intruders.

Coleridge was living at Nether Stowey (between Bridgwater and Minehead). It is unclear whether the interruption took place at Culbone Parsonage or at Ash Farm. He described the incident in his first publication of the poem:

“On awakening he appeared to himself to have a distinct recollection of the whole, and taking his pen, ink, and paper, instantly and eagerly wrote down the lines that are here preserved. At this moment he was unfortunately called out by a person on business from Porlock, and detained by him above an hour, and on his return to his room, found, to his no small surprise and mortification, that though he still retained some vague and dim recollection of the general purport of the vision, yet, with the exception of some eight or ten scattered lines and images, all the rest had passed away like the images on the surface of a stream into which a stone has been cast, but, alas! without the after restoration of the latter!”

English poet and essayist Thomas De Quincey speculated, in his own Confessions of an English Opium Eater, that the mysterious figure may have been Coleridge's physician, Dr. P. Aaron Potter, who regularly supplied the poet with laudanum. However, this story is by no means universally accepted by scholars. It has been suggested by Elisabeth Schneider (in Coleridge, Opium and "Kubla Khan", University of Chicago Press, 1953), amongst others, that this prologue, as well as the Person from Porlock, was in fact fictional and intended as a credible explanation of the poem's seemingly fragmentary state as published. The poet Roger McGough also suggested this view in one of his own poems, saying "I think he got stuck."

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. It was admitted much later that the "friend" was the author himself. In that case, the invented letter solved the problem that Coleridge found little receptiveness for his philosophy in the England of that time.