Cadwallon ap Cadfan was king of Gwynedd and a major opponent of Northumbrian expansion in the early seventh century. Allied with Penda of Mercia, he defeated and killed Edwin of Northumbria at the Battle of Hatfield Chase in 633. His campaign in Northumbria ended when Oswald defeated and killed him at Heavenfield the following year.
Novels about the rise of seventh-century Northumbria often cast Cadwallon as the principal enemy of Edwin or Oswald, but his actions also reflected a struggle against Northumbrian domination in northern and western Britain. Fiction can therefore present him either as a destructive invader or as a ruler attempting to recover power after exile and defeat. The sparse and partisan sources leave considerable room for interpretation.