Arawn is a Welsh/Celtic god of the Underworld and death. He was Lord of Annwfn. He befriended Pwyll when the two encountered each other in the woods. Arawn offered Pwyll to take his for a year and a day, where Pwyll would be transformed to look like Arawn so Pwyll could fight Havgtan. Havgtan happens to be another Lord of Annwfn and enemy of Arawn. Pwyll killed Havgtan.
Pwyll also pretended to be the husband of Arawn's beautiful wife and did not take advantage of the situation. For both killing Havgtan and not having sex with his wife, Arawn rewarded Pwyll. The two became good friends and allies and some believe Arawn sent the goddess Rhiannon to become Pwyll's wife. Pigs were also given to Pwyll's son Pryderi by Arawn.
Arawn is also said to possess the magic cauldron a particular character called Arthur tried to steal.