The Twrch Trwyth

The Twrch Trwyth, a nobleman transformed into a giant boar, is one of the more prominent characters in Welsh myth. In the tale of Culhwch and Olwen he is hunted by Arthur and his men, but not even these great heroes can vanquish this most terrible of enchanted beasts. So why is the Trwch Trwyth so impossible to kill?