Somewhat restricted by his mother ARIANRHOD, who’d given birth in circumstances she did not like to discuss. As a consequence, she did a most unmotherly thing and cursed her son:
1) He could not be called by any name until she said so.
2) He must not play with weapons.
3) He could never marry a human wife.
You will find out more about him under BLODEUEDD. But there is a postscript. After he had been turned into an Eagle, his kind uncle GWYDDION tracked him down, cured his wounds and restored him to human shape.
Since then LLEU has tended to stay out of the public eye and may only be seen at his own convenience.