Blunderbore is a giant of Cornish and English folklore. A number of folk and fairy tales include a giant named Blunderbore, most notably "Jack the Giant Killer". The stories usually associate him with the area of Penwith.
Cornish folklore remembers Blunderbore as living in Ludgvan Lese (a manor in Ludgvan), where he terrorized travelers heading north to St Ives.In "Jack the Giant Killer" he is the second or third giant (along with his brother Rebecks) killed by the hero Jack. Under the influence of that story, the name "Blunderbore" is frequently appropriated by other legendary giants; the later fairy tale "Tom the Tinkeard", a local Cornish variant of "Tom Hickathrift", contains a similar account of the hero's battle with a giant named Blunderbore. Likewise, it is usually given as the name of the giant in "Jack and the Beanstalk".