Llywarch ap Hyfaidd was the king of Dyfed

Kingdom of Dyfed

The Kingdom of Dyfed is one of several Welsh petty kingdoms that emerged in 5th-century post-Roman Britain in south-west Wales, based on the former Irish tribal lands of the Déisi from c 350 until it was subsumed into Deheubarth in 920. In Latin, the country of the Déisi was Demetae, eventually to...

, Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

 until its conquest in 904 or 905 by Cadell ap Rhodri

Cadell ap Rhodri

Cadell ap Rhodri was the son of Rhodri Mawr . He inherited the kingdom of Seisyllwg from his mother Angharad of Seisyllwg in 878, and passed it to his son, Hywel Dda , on his death in 909. Cadell and Hywel had previously conquered Dyfed in 904/905, establishing Hywel as the king in that region...

 and his son Hywel Dda

Hywel Dda

Hywel Dda , was the well-thought-of king of Deheubarth in south-west Wales, who eventually came to rule Wales from Prestatyn to Pembroke. As a descendant of Rhodri Mawr, through his father Cadell, Hywel was a member of the Dinefwr branch of the dynasty and is also named Hywel ap Cadell...

, rulers of Seisyllwg. Kingship passed briefly to his brother, Rhodri

Rhodri ap Hyfaidd

Rhodri ap Hyfaidd was briefly the king of Dyfed. After his brother Llywarch was killed by Hywel Dda and his father Cadell, Rhodri reigned briefly before he himself was killed and the throne was usurped by Hywel, under whom the kingdom then merged with Seisyllwg to form Deheubarth)....

, until rule was consolidated by Hywel. Hywel married Llywarch's daughter, Elen, to legitimise his claim to the throne. He subsequently merged Seisyllwg and Dyfed into the new kingdom of Deheubarth.