It is spelled Atroys (where -t- stands for the sound /th/) in the 10th century Welsh Harleian genealogies and Athruis in the early medieval Latin Liber Landavensis.
The name is etymologically related to that of the figure Andres[us] (where -d- once again stands for the sound /th/) son of Morcant[us] who appears in the early medieval Latin Life of St Cadoc, concluding that both names derive from an Archaic Welsh spelling *Antrēs.
Wendy Davies concluded that Athrwys predeceased his father and thus never ruled as king, and when Meurig died after a long reign the kingship passed to Morgan.
Some writers have identified Athrwys ap Meurig as a potential historical basis for King Arthur.
Critics of this theory point out that the Annales Cambriae reports the death of Ffernfael son of Ithael in 775.