Piran

As LornaMary said, there are several spellings that have been and are currently used (especially throughout Cornwall and many place names in Cornwall are derived from Piran) and Saint Piran was almost certainly original Irish, but I have only ever heard of the name being derived from the Irish name Ciaran like the entry says (rather than Peter); I think what is most commonly believed is that he was called Ciaran in Ireland and because of differences between the Irish and Cornish languages, the C somehow became a P and Ciaran became Piran. As mentioned on Wikipedia: "This was due to the widely recognised ability of the P-Celtic or Brythonic letter 'P' to transform into the Q-Celtic or Gaelic letter 'C'". And as Cornish is a 'Brythonic' Celtic language whilst Irish is a 'Gaelic' Celtic language, that certainly makes sense. The flag of Cornwall (which is black with a white cross through the centre) is also officially called Saint Piran's Flag. :)

St. Pirin, believed born in the 4th or 5th century. Legend has it St.Piran was thrown from the cliffs of Ireland by chieftains, he floated across the Celtic sea on a millstone, to land at Perranporth beach and built an oratory. He charmed people and discovered how to smelt tin by lighting a fire from which the hot black stone gave forth a stream of white liquid. He lived for 200 years and met his end by falling down a well, drunk. (Eileen Carter) In the Shadow of St Piran. Several spellings of the name: Piran, Pirrin, Perran and Peran. Said to be derived from Peter, the rock.