The blob was placed in a chest by Gwydion, Arianrhod's brother. Arianrhod created three geases: only she could give him a name; only she could give him weapons; he would have no human wife. Arianrhod denied him the three aspects of masculinity.
Gwydion raised him anyway, even without a name. Later Arianrhod saw him killing a wren with a single stone. She said that he was a bright lion with a sure hand and he took the name Llew Llaw Gyffes ("bright lion with a sure hand"). Gwydion then tricked her into arming him.
Llew created his own woman out of flowers, Blodeuwedd. Blodeuwedd had an affair with Goronwy and tricked the secret of his death out of him, since Llew could not be killed during the day or night, nor indoors or outdoors, neither riding nor walking, not clothed and not naked, nor by any weapon lawfully made.
He could only be killed at dusk, wrapped in a net with one foot on a cauldron and one on a goat and a weapon forged during the hours when forging weapons was forbidden. She then led him to his death.
Llew became an eagle, but then Gwydion switched him back to human. He killed Goronwy and Gwydion turned Blodeuwedd into an owl.