Gwion was the name given to the son of Gwreang who was left by Ceridwen to stir her cauldron. Drops from the cauldron landed on his finger which he sucked and at once understood everything that had happened or was to happen. He fled to avoid Ceridwen, both pursuer and pursued changing into different shapes. Gwion eventually changed himself into a grain of wheat and she changed herself into a hen and swallowed him. She became pregnant with him and bore him as Taliesin. All this may represent an initiatory process, as C. Matthews suggests in some of his works.

Gwion and the legendary Taliesin appear to be the same character throughout most works.

A certain similarity may be noted between Gwion and the Irish hero Finn (Fionn) mac Cool, who sucked his thumb when some of the essence of the Salmon of Knowledge was on it. The chewing of the thumb may recall a pagan practice of divination. R. Graves states that Gwion was truly a historical person who discovered poetic mysteries and began to compose poetry, using the name of the legendary Taliesin. In many modern works, Gwion makes appearances in relation to King Arthur, but in older manuscripts there was no relation or connection.