Hafgan: HAV-gan
Welsh: "Summer-White"?
In The Mabinogion, a ruler of Annwfn and enemy of Arawn. When Pwyll foolishly chased the White Hart and fought Arawn's Cwn Annwn, he was forced to take Arawn's place against Hafgan in a move which may have had an influence on Sir Gawain and the Green Knight, for the only way to defeat Hafgan was to behead him. This Pwyll did, winning Arawn's trust.