Hwyel Dda
Hywel Dda (Hywel The Good) is remembered both for being a successful ruler in bringing much of Wales under his control, and for codifying the law.
Hywel Dda was the grandson of Rhodri the Great and like his late relative, he combined much of modern-day Wales under his banner.
His father, Cadell ap Rhodri, gave him Dyfed having conquered the kingdom, and his claim was strengthened by his marriage to the last king of Powys' daughter, Elen.
Cadell died in 909, dividing Seiswllwg between Hywel and his brother, who died in 920. Thus, Hywel ruled Dyfed and Seisyllwg and decided to combine them into one kingdom, Deheubarth.
His cousin, Idwal Foel was ruler of Gwynedd until his death in battle in 942. Hywel invaded Gwynedd and exiled Idwal's sons, and wrested Powys from Llywelyn ap Merfyn also in 942.
But it was his approach to state building that cemented his place in history. He developed pragmatic relationships with English rulers to such an extent that he became the only Welsh monarch to issue coins from a mint in Chester.
He assimilated ideas about government from both visiting Rome and studying English law. At a conference in about 945 at Whitland in modern day Carmarthenshire, Welsh law was codified and written down - and it wasn't until the 16th century that English law took precedence.
Hywel Dda died in 950 and his kingdoms were split - Gwynedd returning to the sons of Idwal Foel and Deheubarth and Powys between his sons.
