Rhydderch ap Iestyn was king of Gwent and Morgannwg in south 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...

 and later took over the kingdom of Deheubarth and controlled Powys.

Comparatively little has been recorded about Rhydderch ab Iestyn in the annals. He appears to have originally been ruler of Gwent and Morgannwg, where his son later continued to have his power base. When Llywelyn ap Seisyll

Llywelyn ap Seisyll

Llywelyn ap Seisyll was a King of Gwynedd and of Deheubarth in north-west and south-west Wales, also called King of the Britons by the Annals of Ulster. Also called Llywelyn ap Seisyllt- Lineage :...

, king of Gwynedd

Kingdom of Gwynedd

Gwynedd was one petty kingdom of several Welsh successor states which emerged in 5th-century post-Roman Britain in the Early Middle Ages, and later evolved into a principality during the High Middle Ages. It was based on the former Brythonic tribal lands of the Ordovices, Gangani, and the...

 and Deheubarth died unexpectedly in 1023, Rhydderch was able to seize Deheubarth, apparently by force of arms. In 1033 Rhydderch is recorded by Brut y Tywysogion

Brut y Tywysogion

Brut y Tywysogion is one of the most important primary sources for Welsh history. It is an annalistic chronicle that serves as a continuation of Geoffrey of Monmouth’s Historia Regum Britanniae. Brut y Tywysogion has survived as several Welsh translations of an original Latin version, which has...

 as having been slain by the Irish, but with no explanation of the circumstances.

The kingdom of Deheubarth returned to the original dynasty in the form of Hywel ab Edwin

Hywel ab Edwin

Hywel ab Edwin was king of Deheubarth in south Wales from 1033.Hywel was the son of Edwin ab Einion and great-grandson of Hywel Dda. When the previous king, Rhydderch ap Iestyn, who had usurped the throne, died in 1033 Hywel became king of Deheubarth, sharing the realm with his brother Maredudd.On...

 and his brother Maredudd. A battle between Hywel and his brother and the sons of Rhydderch is recorded the following year. In 1045 Rhydderch's son, Gruffydd ap Rhydderch

Gruffydd ap Rhydderch

Gruffydd ap Rhydderch was a king of Gwent and part of the kingdom of Morgannwg in south Wales and later king of Deheubarth.Gruffydd was the son of Rhydderch ab Iestyn who had been able to take over the kingdom of Deheubarth from 1023 to 1033...

 was able to seize Deheubarth from Gruffydd ap Llywelyn

Gruffydd ap Llywelyn

Gruffydd ap Llywelyn was the ruler of all Wales from 1055 until his death, the only Welsh monarch able to make this boast...

and held it for ten years until Gruffydd regained it.