In Welsh romance Culhwch and Olwen, Ysbaddaden is the father of the beautiful Olwen. He is cursed to die when his daughter marries, so when Culhwch comes to court her, he is naturally perturbed. He tries to kill Culhwch a number of times but ends up more injured than his aspiring son in law. He then gives Culhwch a series of extraordinarily difficult tasks, which Culhwch completes (at least to satisfaction) with the help of King Arthur and his men. When Culhwch returns, Ysbaddaden is beheaded by Culhwch's kinsman Goreu , whose family Ysbaddaden had mistreated severely in the past.

Ysbaddaden is described as a typical evil giant of Celtic storytelling, residing in a magic castle that seems to get farther away the closer one gets to it and requiring forks to hold open his eyes. He is one of the most typical and memorable of his type.