In Welsh mythology, Olwen is the daughter of the giant Ysbaddaden. She is the heroine of the story Culhwch and Olwen in the Mabinogion.

Her father is fated to die if she ever marries, so when Culhwch comes to court her, he is given a series of immensely difficult tasks he must complete before he can win her hand. With the help of his cousin King Arthur, Culhwch succeeds and the giant dies, allowing Olwen to marry her love.

The name "Olwen" reappears in the folktale Einion and Olwen, about a shepard who travels to the Otherworld to marry Olwen. The tale was collected at the turn of the 20th century but is certainly related to Culhwch and Olwen.