Náthairr

 And Náthairr emerges from the seas of flames with his jaw opened wide. He roars and deafens all of the Isles who, in their pain, cried. And because of the serpent 's doing our beloved Oínor died. 

Náthairr, also called the Devouring Serpent or the Great Wyrm is a gigantic grey serpent born from Caedorcha and Unbrangda. Náthairr roams the fire seas of an Drámhoìla Olc ( The Evil Wastes, realm of the dead and home of Caedorcha and the Scourged. ) Náthairr kills the warrior god Oínor during Na Hammána Deíridhe.