What is "gofannon"

Gofannon is a Middle Welsh reflex of Gobannus, one of the deities worshipped by the ancient Celts. He features in Middle Welsh literature as a great metal worker and as the son of Dôn. His name can be compared with the Old Irish gobae ~ gobann ‘ smith,’ Middle Welsh gof ~ gofein ‘ smith,’ Gallic gobedbi ‘with the smiths,’ Latin faber ‘ smith’ and with the Lithuanian gabija ‘sacred home fire’ and Lithuanian gabus ‘gifted, clever’. His apparent counterpart in Irish mythology, Goibniu, in addition to his duties as a smith, also takes on the role of a divine hero who brewed an ale of immortality, in addition to being an architect and builder.

In Welsh mythology, Gofannon killed his nephew, Dylan Ail Don, not knowing who he was. One of the tasks given to Culhwch if he were to win the hand of Olwen was to get Gofannon to sharpen his brother Amaethon's plough.