Hey, a little poking around on the internet was all it took, and now I know who Cu Roi was:
CU ROI MAC DAIRE
(coo' r" e moc da'i re) A powerful chieftain in Munster with great otherworldly powers. He appropiated many otherworldly Hallows which the Ulsterman had captured, including his wife, Blanaid, loved by CuChulain. She deceived him and enabled CuChulain to kill him. Cu Roi disguised himself as the Wild Herdsman and challenged the heroes of Ulster to play the Beheading Game with him.
He is the Celtic prototype of the Green Knight. His death was avenged by Lugaid, his son
(from "The Encyclopedia of the Celts" at www.ealaghol.demon.co.uk
