His biography is vague, but he was regarded as an important ancestor figure for several kingly lines in the Hen Ogledd or "Old North" of Britain.
[3] The Bonedd Gwŷr y Gogledd, a later genealogy of northern kings, gives a modified version of Dyfnwal's family tree.
[4] Here, he is the son of Idnyued and the grandson of Maxen Wledig, better known as the Roman usurper Magnus Maximus.
The Bonedd follows the Harleian in making Dyfnwal the great-grandfather of Rhydderch Hael, a later king of Alt Clut, but his other descendants are altered significantly.
[4] A highly confused track makes Dyfnwal the ancestor to the family of Áedán mac Gabráin, a 6th-century ruler of the Gaelic kingdom of Dál Riata.