A friendship between the two realms is retained long after Pwyll's death; in the fourth branch, Pryderi, Pwyll's son and lord of Dyfed has received a gift of otherworldly pigs from Arawn.
Gwawl, son of Clud, is initially mentioned in the first of the Four Branches of the Mabinogi, when Rhiannon tells Pwyll, Prince of Dyfed, who wishes to marry her, that she is intended for Gwawl.
The novel is a retelling of the story of the First Branch of the Mabinogion, Pwyll Pendefig Dyfed (Pwyll, Prince of Dyfed), and hence is chronologically the first of Walton's Mabinogion novels, though published last.
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Pwyll, the prince of Dyved, offends Arawn, ruler of Annwn (the underworld), by baiting his hunting hounds on a stag that Arawn's dogs had brought down.
The Cauldron of Khath Meigol and its powers of resurrection hark back to Welsh mythology's tale of the Cauldron of Annwn, and a number of the deities seem to have Celtic or Welsh roots: Paul is known as Pwyll after his sacrifice, while Macha and Nemain come straight from Irish mythology.