Eufydd fab Dôn
Eufydd fab Dôn is a minor figure in Welsh mythology, the son of the mother goddess Dôn and brother to the better-known figures of Gwydion, Amaethon, Gofannon and Arianrhod. He is generally believed to have derived from the Gaulish god Ogmios and is cognate to the Irish hero Oghma Grianainech.
Role in Welsh tradition 
Eufydd appears in a number of Welsh texts, spelled variously as Euuyd, Eueyed, Euyd and Ieunydd. He appears twice in the Book of Taliesin; first in Prif Gyfarch Taliesin in which it is stated:
- I have been with skilful men
- With Matheu and Gofannon
- With Eunydd and Elestron
- In company with Achwyson,
- For a year in Caer Gofannon.
and then again in Marwnat Aeddon:
- When Aeddon come from the country of Gwydyen, the thickly covered Seon.
- A pure poison came four nightly fine-night seasons.
- The contemporaries fell, the woods were no shelter against the wind on the coast.
- Math and Euuyd, skilful with the magic wand, freed the elements.
- In the life of Gwydion and Amaethon, there was counsel.
The implication is that Eufydd was remembered in Welsh tradition as a skilled magician, intimately associated with his more illustrious brothers Gwydion and Gofannon, and with his uncle Math fab Mathonwy.
Eufydd also appears in the genealogical tract Bonedd yr Arwyr (The Descent of the Saints) in which he is listed among the children of Dôn.
Associations with Hefeydd Hen 
- Rhys, John. "All around the Wrekin" Y Cymmrodor. vol. XXI. 1908. p 62.
- W. FSkene, Four Ancient Books of Wales. I. p 286-287.
- W. FSkene, Four Ancient Books of Wales.
- Anwyl,Edward. The Four Branches of the Mabinogi.