Dan is the brother of Bendigeidfran and Branwen, and Efnisien's half brother. Following Branwen's marriage to Matholwch, king of Ireland, Efnisien triggers years of battle between the two nations.

In the final bloody battle in Ireland, Dan's brothers are killed and his sister, Branwen, dies of a broken heart. Only seven soldiers manage to escape from Ireland with their lives - Dan and Pryderi are two of them.

After spending seven years on the island of Gwales after the battle, they both eventually return to Pryderi's home in Britain, where Pryderi's mother, Rhiannon - by now a widow - is waiting for them. Dan and Rhiannon fall in love, and despite Llwyd's efforts to make their lives difficult, they both live happily ever after.