Dylan eil Ton Welsh
: "dark son of the wave
Featured in the Mabiogion tale "Math fab Mathonwy," he is the son of Arianrhod and Gwydion, and twin of Lleu Llaw Gyffes. Legend says that at birth, he instantly set off for the sea, and was later killed by his uncle Gofannon, called one of the Three Fatal Blows of Britain. (However, the offical triad does not record this.)
Taliesin is attributed with a poem about him, called "Marwndat Dylan eil Ton--The Elegy of Dylan son of the Wave."