The Person from Porlock was a visitor on Samuel Taylor Coleridge during his writing of the oriental poem Kubla Khan. The reason why his importance has been noted in history is that Coleridge had an idea on how to finish the poem but was interupted by this visitor from Porlock. So Kubla Khan turned out different from what Coleridge originally envisioned. This shows not only the fickle nature of human creativity and how one small detail can change history. In Coleridge's own words, published with 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!

It is possible, of course, that this prologue, as well as the Person from Porlock, is intended to require as much 'suspension of disbelief' on the part of the reader as does the poem itself...

Porlock is at the South West of England, near Exmoor.

The episode was parodied in the novel Dirk Gently's Holistic Detective Agency by Douglas Adams where a time-traveller becomes the Man from Porlock to deliberately prevent Coleridge from completing the poem.