Gwydion fab Dôn is the great conjuror of Welsh mythology, the son of the goddess Dôn and the central figure of the Fourth Branch of the Welsh Mabinogi. His primary association is with the north Welsh kingdom of Gwynedd, where Caer Dathyl — his stronghold, tentatively identified with the promontory fort at Dinas Dinlle near Caernarfon — served as the base for his schemes and sorceries. The Milky Way is still called Caer Wydion (‘Gwydion’s Castle’) in Welsh, preserving his cosmological dimension.
The story
His most celebrated feat of trickery was the creation of phantom war spoils — horses, hunting dogs, and golden shields conjured from toadstools and leaves — to provoke Pryderi of Dyfed into single combat, enabling him to steal the magical pigs of the Otherworld. More morally troubling is his role in the assault on Goewin: Gwydion manufactured a false war to distract Pryderi and cover his brother Gilfaethwy’s crime, for which King Math transformed both men into successive pairs of animals — deer, boar, wolves — forcing them to live together, mate, and return to Math bearing animal offspring for three years as punishment.
It is in the role of father-protector that Gwydion is most sympathetically drawn. After his sister Arianrhod placed three curses on her son Lleu Llaw Gyffes, Gwydion used magical deception at each turn to provide the boy with a name, weapons, and ultimately a wife made from flowers. When Lleu was betrayed and transformed into a dying eagle perched high in an oak tree in the mountains of Gwynedd, it was Gwydion who tracked the eagle, sang three englyns to coax it down, and restored him to human form. Lleu’s recovery is located in the Fourth Branch at a site in the shadow of the mountains near Nantlle, fixing the legend firmly in northwest Wales.