Llywarch Hen was the son of Elidurus, chief of Argoed (in the Rheged region, later Cumberland). In the genealogy known as "Bonedd Gwŷr y Gogledd (The Descent of the Men of the North)" he is listed as a descendant of Coel Hen (King Cole), and is first cousin to King Urien Rheged. It is thought that he may have been a monarch himself, with Urien ruling northern Rheged, and Llywarch ruling the south. In his 1953 book "The Derbyshire Dales", Norman Price links Llywarch to Carl Wark near Sheffield.