Pwyll Pen Annwn is a prominent figure in Welsh mythology and literature, the lord of Dyfed, husband of Rhiannon and father of the hero Pryderi. He is the eponymous hero of Pwyll Pendefig Dyfed, the first branch of the Four Branches of the Mabinogi, and also appears briefly as a member of Arthur's court in the medieval tale Culhwch ac Olwen. Pwyll, Prince of Dyfed also carries many similarities to the Mabinogi Branwen.
This tale is one of a group found in The Mabinogion, one of the earliest known efforts to form a collection of traditional Welsh tales. Such tales, which date back to circa 1325 C.E., were originally passed from person to person and generation to generation orally. The Celtic oral tradition lasted for several centuries and is a possible reason for the abundance of errors and discrepancies found in The Mabinogion as well as other Welsh literature dating back to the fourteenth century or earlier. Professor Sioned Davies of Cardiff University explains the importance of the Celtic oral tradition, in appreciating Welsh literature, this way; "The Mabinogion were tales to be read aloud to a listening audience--the parchment was "interactive" and vocality was of its essence. Indeed, many passages can only be truly captured by the speaking voice."
While hunting in Glyn Cuch, Pwyll, prince of Dyfed becomes separated from his companions and stumbles across a pack of hounds feeding on a slain stag. Pwyll drives the hounds away and sets his own hounds to feast, earning the anger of Arawn, lord of the otherworldly kingdom of Annwn. In recompense, Pwyll agrees to trade places with Arawn for a year and a day, taking on the lord's appearance and takes his place at Arawn's court. At the end of the year, Pwyll engages in single combat against Hafgan, Arawn's rival, and mortally wounds him with one blow and earns Arawn overlordship of all of Annwn. After Hafgan's death, Pwyll and Arawn meet once again, revert to their old appearance and return to their respective courts. They become lasting friends because Pwyll slept chastely with Arawn's wife for the duration of the year. As a result of Pwyll's successful ruling of Annwn, he earns the title Pwyll Pen Annwfn; "Pwyll, head of Annwn."