Arawn was the Lord of Annwfn (Otherworld) in the First Branch of the Mabinogi – Pwyll Lord of Dyved (Mabinogion). Arawn befriended Pwyll when they encountered one another in the woods. Arawn offered Pwyll to take his place as Lord of Annwfn for one year and a day. Pwyll would be transformed to look like Arawn, so that Pwyll could fight Havgtan (Hafgan) in his place. Havgtan was also a Lord of Annwfn and Arawn's archenemy. Havgtan could only be killed in one blow, for the second blow would magically heal Havgtan. So Pwyll mortally wounded Havgtan and refused to strike another blow, so Arawn's enemy died.
Arawn had a beautiful wife, who was unnamed. While Pwyll was pretending to be her lord and husband, Pwyll did not take advance of it, making love to Arawn's wife. Arawn was surprised that Pwyll would protect his wife's chastity, that they became friends and allies. Arawn richly rewarded Pwyll for both deeds. It is believed that Arawn had sent Rhiannon to become Pwyll's wife.
Arawn had also given pigs to Pryderi, Pwyll's son, when Pryderi became Lord of Dyved. These pigs were stolen by Gwydyon (Gwydion), in the Fourth Branch of the Mabinogi – Math Son of Mathonwy. This led to a war between Dyved and Gwynedd, where Pryderi was killed in single combat against Gwydyon, the nephew of King Math of Gwynedd.
Arawn was also said to possess the magic cauldron, which Arthur tried to steal in the obscure poem in the Book of Taliesin, called Spoils of Annwfn (Preiddiau Annwfn).
A story from the Arthurian myths tells how the Pendragon entered Annwn to steal a magick cauldron belonging to Arawn. The quest was a perilous one, and Arthur lost most of his company during the expedition. However, the purpose was an honest one, for the cauldron had life-giving properties and was used to restore the injured King Pellam and his lands. This is the origin of the Grail story.
Restoring the barren lands was an act of worship and healing to the Goddess. Arawn evidently harboured no ill will against Arthur for the trespass, for the Pendragon's entry into Annwn after Camlann met no hindrance. These tales tell us much about Arawn and his people, and it is clear that the ælves believe that kindnesses must be repaid and injustices remedied.
By clothing himself in grey robes, Arawn reminds us that people and things are not always what they seem. Greatness is not measured by material possessions, nor is it the ability to wield one's power. Arawn shows understanding and compassion, and this makes him a great leader. This is not to say he allows injustices to pass by; he does not. The realm of the ælves is all about actions and consequences.
Arawn shows us the importance of acknowledging his realm and its inhabitants, for to fail to do so denies us the opportunity to form rewarding friendships that transcend the boundaries between our worlds. Incurring the wrath of the faeries can have severe consequences, as shown in the Arthurian tales. Yet avoiding their displeasure is not difficult, and Arawn reveals the moral nobility by which we should live.