Arawn is a Celtic Welsh god that is the leader of the underworld. He is talked about in the Mabinogion from the Story of ‘Pwyll Lord of Dyfed’ and also in ‘The Spoils of Annwn’.
Pwyll meets the god when he is out hunting around the fringes of his kingdom, and irritates Arawn by allowing his hounds to be free on a stag currently being hunted by him.
Ultimately they get into a bargain were they will exchange places for 12 months in each others form.
Pwyll will become Lord of the Underworld, and Arawn gets to be the Lord of Dyfed.
During this period Pwyll slays Hafgan a foe of Arawn that has been bothersome to his kingdom.
They each turn out to be firm allies simply because neither of them sleeps with the others spouse throughout their trade.
Arawn was as well the master of a magical cauldron with rejuvenating power, that would not boil a coward’s food. Arthur led a mission in to Annwn, Arawn’s Kingdom, to steal this treasured artefact. Arawn is additionally the guardian of the magical creatures inside his kingdom.
In lots of ways Arawn is a similar figure to Gwynn ap Nudd, they are both chiefs of the wild hunt and gods of the underworld. Their group of hounds share exactly the same characteristics, and Gwynn ap Nudd furthermore takes part in trades with other people.
Most likely they are 2 names for a similar archetype.