Our chief reference to Owain is in the poems of Taliesin, Urien's bard. The poem GWEITH ARGOED LLWYFAIN (the battle of Argoed Llwyfain) tells of Owain's part in a battle between the men of Rheged under Urien and the men of Northumbria under "Fflamddwyn" or Firebrand, possibly the Anglian king Theoderic. When Fflamddwyn demands hostages, Owain shouts defiance and inspires the men of Rheged to fight rather than give tribute to the English. Taliesin also composed MARWNAD OWAIN, an elegy to Owain, which suggests, as no elegy to Urien exists or has survived, that Owain predesceased his father and was never king of Rheged. In the poem it is said that Owain slew Fflamddwyn-
Pan laddodd Owain Fflamddwyn Nid oedd fwy nogyd cysgaid Cysgid Lloegr llydan nifer A lleufer yn eu llygaid A rhai ni ffoynt haeach A oeddynt hyach na rhaid Owain a'u cosbes yn ddrud Mal cnud yn dylud defaid When Owain slew Fflamddwyn it was no more to him than to sleep The wide host of Lloegr(England)sleeps with the light in their eyes And those that did not flee were braver than was needed Owain punished them harshly like a pack of wolves chasing sheepIn later times Owain was drawn into the Arthurian cycle of legends, appearing in the Mabinogion tale of the Lady of the Fountain and appearing in Sir Thomas Malory's Le Morte d'Arthur as Sir Uwain.