Ystrad Tywi
Rhys was the son of Owain ab Edwin of the line of Hywel Dda, and member of the Dinefwr dynasty. He followed his brother Maredudd as king of Deheubarth in 1072. Together with the nobility of Ystrad Tywi, he was implicated in the killing of Bleddyn ap Cynfyn king of Gwynedd and Powys in 1075.