Brother of Gwydion, he fell in love with Goewin, the maiden footholder of his uncle Math ap Mathonwy. So what does he do? He gets his brother to stage a war, and then rapes Goewin. For this, Math turns the brothers into pigs, deer, and wolves, forcing them to mate with each other.
As a god, there is little said; he is generally Gwydion's sidekick.