Hychddwn Hir (from the Welsh hych, "Swine" and hir, "Long") appears in the fourth of the Four Branches of the Mabinogi and is one of the three sons of Gwydion and Gilfaethwy. As punishment for the rape of Goewin, Math banished his nephews, turning them into a breeding pair of deer for a year, then wolves, and finally pigs. They had three children over the three years: Hyddwn, Hychddwn, and Bleiddwn. Hychddwn is the offspring of the pig pairing. Math took him and transformed him into a human being, baptising him Hychddwn Hir ("Tall piglet").
References
Hychddwn Wikipedia(Text) CC BY-SA