Of all the strange births in the Mabinogi — and the Mabinogi has a lot of strange births — none is stranger than that of Dylan Ail Don, 'Dylan Second Wave', the brother of the great hero Lleu Llaw Gyffes.
His mother was Arianrhod, daughter of Dôn, herself a sea-and-stars goddess of immense pride. The story is told in the Fourth Branch of the Mabinogi. Arianrhod has been put forward as a candidate for the role of foot-holder to King Math of Gwynedd — a sacred position that requires the holder to be a virgin. Asked to step over the king's wand to prove her status, she does — and immediately drops two children to the floor of the court. The first is a strong, fair, golden-haired boy. The second is barely glimpsed before he makes for the door.
That second child is Dylan. He runs straight from the king's hall to the sea, plunges into the salt water of the Menai Strait, and at once takes its nature: he swims as well as any fish, the waves carry him, no boat can outrun him, and he can no more drown than a wave itself. The Mabinogi says simply that 'the moment he came to the sea, he received the sea's nature, and swam as well as the best fish that was in the sea.'
He is the original Welsh sea-spirit — the personification of the salt water that surrounds Ynys Môn on three sides. Some scholars read him as a half-remembered fragment of an older Brythonic sea-god, demoted to a mortal hero in the Christian retelling but still trailing his divinity behind him. The waves themselves were said to mourn at his name; the sound of the surf breaking on the rocks of Caernarfon was called Dylan's Death-Groan, the Tonn Dylan, after the moment of his eventual killing by his own uncle Gofannon, the god of smiths, who struck him down by mistake.
His name is woven into the geography of north-west Wales. The Tonn Dylan — Dylan's Wave — was one of the three great waves of Britain. The shore at Maen Dylan, between Clynnog Fawr and Pontllyfni on the Llŷn coast, is said to be the place his body washed up. The poet Dylan Thomas was named, his father insisted, after this Dylan and no other — a small piece of the Mabinogi carried into the twentieth century.
He is one of the great melancholy figures of Welsh myth: born to a goddess, denied a place in her hall, claimed instantly by the sea, killed by his own kin, mourned by the waves themselves. Wear Dylan Ail Don and you wear the salt water of the Menai — beautiful, restless, never quite tame, and never far from Ynys Môn.