In Geoffrey of Monmouth's Historia Regum Britanniae c. 1136, he is only mentioned in passing, as succeeding his uncle, Auguselus (Angusel), King of Albany (northern Scotland).

The settlers of Brittany brought much of their insular British culture when they came to the continent, and in the 12th century, updated versions of Breton lais and stories became popular with French audiences.

In it, the eponymous hero Yvain seeks to avenge his cousin Calogrenant who had been defeated by an otherworldly knight beside a magical storm-making fountain in the forest of Brocéliande.

With the aid of Laudine's servant Lunete, Yvain wins his lady and marries her, but his cousin Gawain convinces him to embark on chivalric adventure.

Yvain goes mad with grief and lives naked in the woods (probably the earliest instance of a hero's mental illness in French literature, which later became a popular motif[2]), but eventually is cured by Morgan and decides to win back his love.

A lion he rescues from a dragon proves to be a loyal companion and a symbol of knightly virtue, and helps him complete his quest, which includes defeating the giant Harpins and two demons.

Chrétien's Yvain had a huge impact on the literary world; German poet Hartmann von Aue used it as the basis for his Middle High German court epic Iwein, while the author of Owain, or the Lady of the Fountain, one of the Welsh Romances included in the Mabinogion, tells essentially the same story, recasting the work in a Welsh setting.

"[6] The chronicle Scalacronica uses the cyclical prose narrative but vastly expands of Yvain's roles in the battle, having him replace Arthur as Mordred's slayer as well as Griflet in the final scenes.

[7] Yvain's birth by the fay (fairy) Morgan may have its roots in Welsh legends: two of the Triads claim the goddess-like figure of Modron as his mother.

In The Dream of Rhonabwy, a Welsh tale associated with the Mabinogion, Owain is one of Arthur's top warriors and plays a game of chess against him while the Saxons prepare to fight the Battle of Badon.