The eponymous hero of the Mabinogion story of the Dream of Rhonabwy.
One of the soldiers of Madawg, ruler of the country of Powys (Wales) in the twelfth century.
While on a mission to capture Iorwerth, Madawg’s renegade brother, Rhonabwy and his companions came to the town of Didylstwn in Rhychdir Powys. There, they asked for lodging at the house of Heilyn the Red.
After receiving a cold welcome in the dilapidated residence, Rhonabwy went to sleep on a yellow ox skin and had a marvelous dream that he and his companions were in the Britain of Arthur, some seven hundred years before his time. They met the warrior Iddawg, who escorted them to Arthur’s camp on the River Severn. There, Rhonabwy and his companions heard of the Battle of Camlann, witnessed a gwyddbwyll game between Arthur and Owain (Ywaine), and saw Arthur make peace with Osla before the battle of Badon.
When Rhonabwy awoke, he found he had been sleeping for three days and three nights.
Source
Breudwyt Rhonabwy | 13th century