Once long ago there was a perfectly ordinary human boy that went by the name of Gwion Bach, who lived as the servant to the goddess of magic, Cerridwen. This goddess had a son of her own who had, sadly, not inherited his mother's looks, personality, intelligence, nor abilities in any sort. Despairing over the cursed hand she had been dealt, Cerridwen was struck with an idea that could fix the lot her child had been dealt. 

There was a forbidden potion that could, when ingested, grant one person infinite wisdom and magical gifts on par with the chieftest of all the gods. 

Though the potion was forbidden, Cerridwen was driven by the love of a mother and so, with the help of her servant boy who she had raised as a second child, she set to work creating it. Every day she would spend hours stirring the potion exactly as it was meant to be stirred, with the ingredients measured and dropped in carefully to prevent spillage. Not a drop was to be lost, she warned Gwion when it was his time to stir the potion all night long, for it was irreplaceable. So the creation of this potion went for months at a time until at long last, at the first full moon of spring's height, was it completed. 

But with all things of this sort there are unforeseen consequences.

The potion was of magical and divine natures both, and so it had a mind of its own. And so that night under the full moon as the gentle winds of spring flowed through the goddesses' mortal dwelling place, it took action. Three drops of the potion leapt from the cauldron to land directly on the back of Gwion Bach's hand. With the scalding hot liquid on his skin, the boy did what any mortal being would and instinctively pressed his mouth to the burns...and unintentionally swallowed the potion. Immediately he was struck with the knowledge of what Cerridwen would do once she discovered his accidental transgression and so he fled, his form changing to that of a rabbit. True to form Cerridwen returned to see the remaining potion had now turned into a deadly poison, for the only parts of it that could be eaten were the three drops, and a missing servant boy. And thus, filled with wrath over a perceived betrayal, she took up the form of a wolf and chased Gwion Bach. 

On and on the chase went, each time Cerridwen drew close her prey would change form to evade her. 

From rabbit to salmon to swallow. Only to be met each time with the goddess' changed form. Wolf, to otter, to falcon. Until finally Gwion fled into a barn and took on the form of a piece of grain...just for Cerridwen, in the form of a hen, to devour him. Ending his life.

However this too was part of the potion's plan and so, nine days later, Cerridwen found herself with a newborn son after nine days of terrible headaches...that she promptly shoved into a sealskin bag and tossed out to sea. 

From there the bag drifted until it ended up in the fishing weir of Prince Elffin of the now long drowned land of Cantre'r Gwaelod. The prince opened the bag and upon seeing the infant boy it held, named the child "Taliesin" for his fair features and shining hair before returning to his father's hall not with a haul of salmon but with a child that was both Fae and partially divine. 

After that... Taliesin grew as all children do. Cantre'r Gwaelod met its sea-driven demise and he began to wander as a bard and a teacher for kings, mages, and any who wished to truly learn.