Arrawn
The name Arawn is used to translate Auguselus, the brother of Urien, in a Welsh version of Geoffrey. The Triads also make mention of an Arawn, son of Kynvarch.
In Welsh tradition Arawn was the name of the King of Annwfn, the Welsh otherworld, in the non-Arthurian tale of Pwyll, but it may also have been the name of Urien’s brother in Welsh legend before Geoffrey wrote his Historia.
After clashing with Pwyll during a hunting incident, the two warriors became friends and agreed to exchange countenances, kingdoms, and wives for a year. Pwyll, however, refused to take advantage of the situation and sleep with Arawn’s wife. Arawn’s mortally enemy, Hafgan, was killed by Pwyll.
R. S. Loomis thought that a number of Arthurian characters showed Arawn’s influence, including the Green Knight and Orguelleuse. In a Welsh version of Geoffrey of Monmouth, Arawn becomes the counterpart of Angusel, Urien’s brother. Arawn may therefore be identical to Aron, Urien’s brother and Arthur’s knight in the Triads.