Myrddin is one of the Twelve Angels of the Creator God, Watos. His opinion of the 'Perfect' world was different from the other Angels. The others chose to exterminate the imperfect to create a new perfect world, but Myrddin's view was the opposite - he prefers correction to extermination. Unlike the other Angels that are eternally youthful, Myrddin is shown to be an elderly man. He explains to Arawn that he doing the acts that is against his own conscience for a very long time. Although it can be assumed that he aided in the genocide of creatures on earth, but deep in his heart he loathes it, hinting that he is the only Angel that is merciful. Because of this, he is considered a senile by his colleagues and even Arawn initially.
He later sacrificed himself to begin a new spring. He also gave the humans the gift of fire to save the human race from the wrath of the other Angels whom began the Ice Age to exterminate them. According to Rhiannon, he is punished severely by the other Angels for his action (similar to Prometheus) and the twilight is caused by the tears of a god as legend claims that Myrddin's suffering is so intense that he weeps, but this maybe just a legend. In 17th episode, Myrddin appears in Arawn's vision and there are no sign of torture on him. And in episode 4, Arawn states that no one can punish him anymore. And, in the last episode, he and Pwyll appear in Rhiannon's vision along with Primula to give support ot her. Although he and Pwyll didn't speak at all, but their presence motivates Rhiannon to save everyone.