Rhacymwri
Half brother of Hygwydd and one of Arthur’s warriors. He had an odd talent and desire for destroying barns that is not quite clear.
He participated in the hunt for Twrch Trwyth and helped to trap him in the Severn river, but was dragged to the bottom by two millstones. He apparently survived, because he later went with Arthur’s party to the cave of the Black Hag in the Valley of Distress. Cacamwri and Hygwydd were sent in first, and were both mauled, stripped, and thrown out of the cave screaming by the Black Hag.
As Rhacymwri he is an attendant of Arthur’s, as well as his brother Hygwyd.
Source
Culhwch and Olwen | Late 11th century