Taliesin is a Celtic God. His story comes from Wales. He is also a son of Cerridwen. His story is quite interesting actually. Cerridwen was brewing a potion for her son Morfran; also known as Afagddu since people got ill when they saw him because of how 'ugly' he was.
Cerridwen makes a young servent boy watch the cauldron (Gwion), while he was stirring the pot three drops of the hot potion splashed on his finger and he put his finger in his mouth to cool it off. Those three drops blessed him with the knowledge within. Cerridwen worked hard to get those ingredients and was not pleased. So she chased him through every season. He turned into a hare, fish, a bird and finally an ear of corn.
Cerridwen turned into a hen and swallowed an ear of corn which was actually Gwion. Nine months later she gives birth to him as Taliesin. She thought about killing him when he was an infant, but she decided to have mercy and threw him into the sea. He was rescued by a Celtic prince named Elphin. He is different from the other gods because there was evidence showing he was a real person. Or at least there was a bard named Taliesin in the 6th century. His writings still exist.
Taliesin is the god of magic, music, poetry, and wisdom. He was also known as the Prince of Song and Chief of the Bards of the West. He was a Patron of Druids and a great magician, bard, and shapeshifter.
To clarify a bit, Taliesin is specifically a Welsh figure, but not a god. In Welsh mythology,Cerridwen is an enchantress andGwion Bach was her servant who attended to the cauldron. The story goes roughly how you presented it, but the important part is that he was a prominent bard and in some cases a magician, but not a god specifically.