He became the sole king of Seisyllwg in 920 and shortly thereafter established Deheubarth, and proceeded to gain control over the entire country from Prestatyn to Pembroke.

The historian Dafydd Jenkins sees in them compassion rather than punishment, plenty of common sense and recognition of the rights of women.

[3] Hywel Dda was a well-educated man even by modern standards, having a good knowledge of Welsh, Latin and English.

The local health board of south-west Wales, covering an area roughly corresponding to the kingdoms of Dyfed and Seisyllwg of which Hywel was King, also bears his name.

[citation needed] This gave Rhodri no standing to claim the kingship of Seisyllwg himself, but he was able to install his son Cadell as a subject king.

[8] Hywel and Clydog seem to have ruled Seisyllwg together following their father's death and jointly submitted to Edward the Elder of England in 918.

Later in his reign, he was able to leverage his close association with Æthelstan and the English crown to great effect in his ambitions within Wales.

Nevertheless, his name continued to be associated with Welsh law which remained in active use throughout Wales until the appointed date of implementation of the Laws in Wales Acts 1535–1542 of King Henry VIII of England who asserted his royal descent by blood-line from Rhodri Mawr via Hywel Dda.

J. E. Lloyd claimed Hywel was an admirer of Wessex,[17] while David Peter Kirby suggests that it may have been the action of a pragmatist who recognised the realities of power in mid-10th century Britain.

[18] A Welsh-language poem entitled Armes Prydein, considered by Sir Ifor Williams to have been written in Deheubarth during Hywel's reign, called for the Welsh to join a confederation of all the non-English peoples of Britain and Ireland to fight the Saxons.