Rhys ap Gruffydd (1132 – 28 April 1197) was the ruler of the kingdom of Deheubarth in south Wales. He is commonly known as The Lord Rhys, in Welsh Yr Arglwydd Rhys, but this title may not have been used in his lifetime. He usually used the title "Prince of Deheubarth" or "Prince of South Wales", but two documents have been preserved in which he uses the title "Prince of Wales" or "Prince of the Welsh". Rhys was one of the most successful and powerful Welsh princes, and after the death of Owain Gwynedd of Gwynedd in 1170 was the dominant power in Wales.
Rhys's grandfather, Rhys ap Tewdwr, was king of Deheubarth, and was killed at Brecon in 1093 by Bernard de Neufmarche. Following his death, most of Deheubarth was taken over by the Normans. Rhys's father, Gruffydd ap Rhys, was eventually able to become ruler of a small portion, and more territory was won back by Rhys's older brothers after Gruffydd's death. Rhys became ruler of Deheubarth in 1155.