Brenin Ddyfed Aergul Lawhir o Ddyfed was mentioned by Gildas who, although he does not provide his name, calls his son Uortiporius the bad son of a good king.
He was of Irish descent, a member of the tribe known as the Déisi, a segment of which moved from Ireland to Wales (hence Allmuiran) at an uncertain date, and eventually became rulers of Dyfed.
Another name for Aergul was Aergul "Long Hand".